Question 1

Is Coagly free?

Accepted Answer

Yes. Coagly is free to download, and dose tracking, your daily dose reminder, appointment reminders for your next INR test, your full history and CSV export are free forever. Coagly Pro is an optional subscription that adds an INR dose calculator and deeper trend insights — interpretation tools, never your basic safety net. Missing a dose because a reminder sat behind a paywall is a real risk, not a place to upsell you.

Question 2

What is a normal INR range?

Accepted Answer

There is no single normal INR. Without an anticoagulant it sits around 0.8 to 1.2. On warfarin, the usual target is 2.0 to 3.0 for atrial fibrillation, DVT and pulmonary embolism, and 2.5 to 3.5 for most mechanical heart valves. Your own range is set by your prescriber, and every reading should be judged against it.

Learn more: Normal INR range chart →

Question 3

What is time in therapeutic range, and what is a good score?

Accepted Answer

Time in therapeutic range (TTR) is the share of your days — not your tests — spent inside your target range. It predicts outcomes far better than any single reading. Above 70% is generally regarded as good control, 65% is the common quality benchmark, and below 60% is treated as poor control. Coagly calculates yours automatically using the Rosendaal method clinics use.

Learn more: Time in therapeutic range →

Question 4

What should I do if I miss a dose of warfarin?

Accepted Answer

If you remember within about 12 hours of your usual time on the same day, take it and carry on normally. If more time has passed, skip it and take only your normal dose today. Never double up to catch up. If you have missed two or more days, contact your anticoagulation clinic. Always record the date — your clinic will want it.

Learn more: Missed a warfarin dose →

Question 5

My INR is too high — how worried should I be?

Accepted Answer

Above your range means a raised bleeding risk, though most people feel nothing at all. Readings of 5.0 or above warrant contacting your clinic the same day even without symptoms, and any head injury needs assessment regardless of your number. Antibiotics, illness, alcohol and eating less vitamin K than usual are the most common causes of a spike.

Learn more: INR too high →

Question 6

Which foods should I avoid on warfarin?

Accepted Answer

Fewer than most people expect. Warfarin needs a steady vitamin K intake rather than a low one, so cutting greens out entirely tends to make control worse rather than better. The bigger problem is swinging — weeks of salads followed by weeks without. Large or regular amounts of cranberry juice and supplements such as St John’s wort are worth avoiding.

Learn more: Warfarin foods & vitamin K →

Question 7

Does my warfarin dose change from day to day?

Accepted Answer

Often, yes, and it is entirely normal. The weekly total you need rarely divides evenly into available tablet strengths, so clinics build a weekly pattern — 5 mg some days, 2.5 mg others. It is also the biggest source of dosing errors, which is why Coagly's reminder names today's actual amount and rewrites itself the moment your prescription changes.

Learn more: Weekly dose schedule →

Question 8

Can I convert a PT in seconds to an INR?

Accepted Answer

Yes. INR = (patient PT ÷ your lab's normal mean PT) raised to the power of the reagent's ISI. Both the normal mean and the ISI belong to the lab that ran your test and are usually printed on the report. Coagly will do the conversion when you log a result, and there is a free converter on this site.

Learn more: PT to INR conversion →

Question 9

How often should I get my INR tested?

Accepted Answer

Every 2 to 4 days when starting warfarin, then weekly to fortnightly while stabilising, and typically every 4 weeks once stable — sometimes stretched to 8 or 12 weeks with a long track record. Testing more often reliably improves time in range: roughly 50 to 60% of patients stay in range with monthly testing versus 77 to 85% with weekly testing.

Learn more: How often to test INR →

Question 10

Can I get my data out of Coagly?

Accepted Answer

Yes, and it is free. Your complete history exports as CSV reaching back to your very first entry — readings, target ranges, notes and dose history. You can also import existing history from another app by CSV, so you are not starting from zero. A record you cannot get out is not a record.

Learn more: INR history for your doctor →

Question 11

Is Coagly available on Android?

Accepted Answer

Yes. Coagly is on Google Play for Android and on the App Store for iPhone and iPad, in English and Spanish. The iOS version requires iOS 16.4 or later. The free web tools on this site — the TTR calculator, PT to INR converter and test planner — also work in any browser on any device, with no install at all.

Question 12

Does Coagly tell me what dose to take?

Accepted Answer

No, and deliberately so. Coagly is a tracking and organisation tool. It records what you were prescribed, reminds you of it and shows you your trends, but dosing decisions belong to your prescriber and your anticoagulation clinic. Never change a warfarin dose on the basis of an app.

Question 13

Is an INR of 2.5 good?

Accepted Answer

For most people taking warfarin for atrial fibrillation, a DVT or a pulmonary embolism, 2.5 is the middle of the usual 2.0 to 3.0 target and is a good result. For someone with a mechanical mitral valve whose target is 2.5 to 3.5, the same 2.5 sits right at the bottom edge of range. Whether a number is good depends on the range you were given, not on the number alone.

Question 14

What INR is dangerous?

Accepted Answer

Bleeding risk climbs noticeably above 4.0 to 5.0, and an INR above 5.0 warrants contacting your clinic the same day even if you feel completely well. On the other side, an INR near 1.0 while taking warfarin means you have very little anticoagulant protection. Both directions need a clinician, not a self-adjustment.

Question 15

Why does my INR change when nothing has changed?

Accepted Answer

Warfarin is unusually sensitive to ordinary life. Vitamin K in your diet, a course of antibiotics, alcohol, illness with fever or diarrhoea, a new supplement and even a change in how well you absorb food can all move it. Recording a short note alongside each reading is often what lets you and your clinic spot the pattern later.

Question 16

Does a home INR meter give the same number as the lab?

Accepted Answer

Home meters are accurate enough to steer treatment and are widely used, but a small difference from the lab value is normal, particularly at higher INRs. Clinics usually check a meter against a lab draw when you start self-testing. What matters most is consistency — record which device produced each reading.

Question 17

What is a good time in therapeutic range?

Accepted Answer

Above 70% is generally regarded as good control, and 65% is the quality benchmark many anticoagulation services work to. Between 60% and 65% is around the average reported in large warfarin trials. Below 60% is usually treated as poor control and prompts a look at what is interfering.

Question 18

How is TTR calculated?

Accepted Answer

With the Rosendaal linear interpolation method. It assumes your INR moved in a straight line between each pair of consecutive tests, assigns every day in between an estimated value, counts how many of those days fall inside your target range, and divides by the total number of days assessed.

Question 19

Can I calculate my own TTR?

Accepted Answer

Yes. You need your target range and your past INR results with the date of each. Our free TTR calculator applies the Rosendaal method and returns your percentage, the split above and below range, and a chart — entirely in your browser, with nothing uploaded.

Question 20

Does a low TTR mean warfarin is the wrong drug for me?

Accepted Answer

Not by itself, but it is a genuine reason to have the conversation. Persistently poor time in range is one of the factors clinicians weigh when considering whether a different anticoagulant would suit you better. Bring the number to your prescriber rather than acting on it.

Question 21

Can I take a double dose of warfarin to catch up?

Accepted Answer

No. Doubling up does not undo the missed day and it pushes your INR above your target two to three days later, when you are no longer expecting it. Take only your normal dose, record the miss, and tell your clinic.

Question 22

How long does a missed warfarin dose affect INR?

Accepted Answer

Typically the drop appears over the following two to four days and recovers across the week after that. Warfarin works by suppressing clotting factor production, so both the loss and the recovery are gradual rather than immediate.

Question 23

What if I missed warfarin for 3 days?

Accepted Answer

Contact your anticoagulation clinic today. Three consecutive missed doses can leave your INR well below your target range and meaningfully reduce your protection against clots. Your clinic will decide how to restart and will likely test you sooner than planned.

Question 24

Should I tell my doctor I missed a dose?

Accepted Answer

Yes, always, and with the specific dates. Missed doses are the most common explanation for an unexpectedly low INR. Without knowing, a clinician may adjust a prescription that was never the underlying problem.

Question 25

Is an INR of 4 dangerous?

Accepted Answer

An INR of 4.0 is above the usual 2.0 to 3.0 target and carries a raised bleeding risk, but it is not an emergency on its own in someone with no bleeding. Contact your anticoagulation clinic for guidance — they may hold a dose and retest sooner. Any active bleeding at this level should be treated as urgent.

Question 26

What INR level causes bleeding?

Accepted Answer

Bleeding risk rises progressively rather than at a single threshold, but it climbs noticeably above 4.0 to 5.0 and steeply above 9.0. That said, serious bleeding can occur at any INR after a significant injury, and many people sit above 5.0 with no symptoms at all — which is why the number, not the symptom, is the early warning.

Question 27

What are the symptoms of a high INR?

Accepted Answer

Most often none. When symptoms appear they include unexplained bruising, nosebleeds, bleeding gums, blood in urine or stool, black tarry stools, unusually heavy periods, and cuts that bleed far longer than expected. Any head injury needs assessment regardless of symptoms.

Question 28

How do I lower my INR quickly?

Accepted Answer

That decision belongs to your clinician. Depending on the reading and whether you are bleeding, they may hold doses, reduce your weekly total, or give vitamin K. Do not stop warfarin or take vitamin K supplements on your own — over-correcting swings you into clot risk instead.

Question 29

Is an INR of 1.5 dangerous on warfarin?

Accepted Answer

It means you have significantly less anticoagulant protection than intended, and it should be reported to your clinic promptly. How urgent it is depends on why you take warfarin — it is treated more seriously in someone with a mechanical heart valve than in someone anticoagulated for a past DVT. It is not an emergency in itself, but it is not something to leave until your next scheduled appointment.

Question 30

What causes a sudden drop in INR?

Accepted Answer

Missed doses are the most common cause. Others include eating more vitamin K than usual, starting a medicine that speeds warfarin’s breakdown such as rifampicin, carbamazepine or St John’s wort, vomiting or diarrhoea shortly after a dose, and following a new dose schedule inconsistently.

Question 31

Should I take extra warfarin if my INR is low?

Accepted Answer

No. The effect of extra warfarin appears two to three days later and frequently overshoots into bleeding risk. Report the reading to your anticoagulation clinic and follow the adjustment they give you.

Question 32

How long does it take to raise a low INR?

Accepted Answer

Usually several days to a week after a dose increase, because warfarin works by suppressing clotting factor production rather than acting immediately. Your clinic will normally retest within a week to see where the change has landed.

Question 33

Can I eat salad on warfarin?

Accepted Answer

Yes. The goal is a steady amount of vitamin K, not none. If salad is part of your normal diet, your warfarin dose has already been balanced around it. What causes trouble is a large swing — weeks of salads followed by weeks without.

Question 34

What foods should be completely avoided on warfarin?

Accepted Answer

Very few need complete avoidance. The ones most often advised against are large or regular quantities of cranberry juice, natto, and supplements such as St John’s wort, high-dose fish oil, ginkgo and dong quai. Green vegetables should be kept consistent rather than eliminated.

Question 35

How much vitamin K can I have on warfarin?

Accepted Answer

There is no universal number, because your dose was set against your own habitual intake. Most services advise keeping vitamin K broadly stable week to week rather than aiming at a target amount. If you want to change your diet significantly, tell your clinic so they can test more often while your dose is rebalanced.

Question 36

Does alcohol affect warfarin and INR?

Accepted Answer

Yes, in both directions. Binge drinking tends to raise INR sharply and adds bleeding risk, while heavy long-term drinking that has damaged the liver can affect it unpredictably. Moderate, consistent intake is generally manageable — the pattern matters more than the total.

Question 37

How do you convert PT to INR?

Accepted Answer

Divide your patient PT in seconds by your lab’s normal mean PT, then raise that ratio to the power of the reagent’s ISI. In full: INR = (patient PT / normal mean PT) ^ ISI. Both the normal mean and the ISI are specific to the lab that ran your test and are usually printed on the report.

Question 38

What is a normal PT in seconds?

Accepted Answer

Most labs report a normal prothrombin time of roughly 11 to 13 seconds, though the exact reference interval varies by lab and reagent. Your own lab’s normal mean is the value you should use in the conversion.

Question 39

What is ISI in an INR calculation?

Accepted Answer

The International Sensitivity Index describes how sensitive a particular thromboplastin reagent is compared with an international reference preparation. It is the exponent in the INR formula and typically falls between 0.9 and 1.7. Without it, a PT ratio cannot be turned into a comparable INR.

Question 40

Is the PT ratio the same as the INR?

Accepted Answer

Only when the ISI is exactly 1.0. For any other reagent the ratio has to be raised to the power of the ISI, and the difference can be clinically meaningful — a ratio of 2.0 with an ISI of 1.2 gives an INR of 2.30.

Question 41

How often should INR be checked on warfarin?

Accepted Answer

Every 2 to 4 days when first starting, weekly to fortnightly while stabilising, and typically every 4 weeks once stable. Some very stable patients are extended to 6, 8 or 12 weeks. Any dose change, new medication or illness should prompt a test within one to two weeks.

Question 42

Can I go 3 months between INR tests?

Accepted Answer

Twelve-week intervals are used, but only for patients with a long documented history of consistently in-range results on an unchanged dose. It is not appropriate shortly after starting warfarin, after any dose change, or for anyone whose readings move around. Your clinic decides.

Question 43

Does testing more often improve control?

Accepted Answer

Yes, substantially. Roughly 50 to 60 per cent of patients stay in range with monthly testing, rising to around 77 to 85 per cent with weekly testing. More frequent testing catches drift before it becomes a long stretch out of range.

Question 44

What happens if I miss an INR test?

Accepted Answer

Book a replacement as soon as you can and keep taking your prescribed dose in the meantime unless told otherwise. A missed test means any drift goes unnoticed for longer, which is one of the quieter ways people end up spending weeks out of range without knowing.

Question 45

Which antibiotics affect warfarin the most?

Accepted Answer

Metronidazole, trimethoprim–sulfamethoxazole and the azole antifungals such as fluconazole have the strongest effect and can raise INR substantially. Quinolones and macrolides have a moderate effect. Rifampicin is the notable exception — it lowers INR rather than raising it.

Question 46

How soon do antibiotics affect INR?

Accepted Answer

Usually from around day three to five of the course, peaking near the end or shortly after it finishes. The delay catches people out — an INR checked on the final day of treatment can miss the peak, so a test in the week afterwards is often worthwhile.

Question 47

Can I take amoxicillin with warfarin?

Accepted Answer

Yes, amoxicillin is commonly prescribed alongside warfarin and its effect is usually mild. It is still variable between individuals, so tell the prescriber you take warfarin and ask whether an extra INR check during the course is warranted.

Question 48

Should I stop warfarin while taking antibiotics?

Accepted Answer

No, not unless your clinician specifically tells you to. Stopping warfarin removes the protection it was prescribed to provide. The interaction is managed with monitoring and, where needed, a temporary dose adjustment decided by your clinic.

Question 49

Why is my warfarin dose different on different days?

Accepted Answer

Because the weekly total you need rarely divides evenly into the tablet strengths available. Alternating amounts across the week — 5 mg some days, 2.5 mg others — lets your clinic hit a precise weekly total. Warfarin acts over several days, so your body responds to the weekly amount rather than any single day.

Question 50

What is a normal weekly warfarin dose?

Accepted Answer

It varies enormously between individuals, commonly from around 10 mg to 70 mg per week, and is influenced by genetics, age, diet, other medications and the condition being treated. There is no normal dose to compare yourself against — only the dose that keeps your own INR in range.

Question 51

Can I take my warfarin at a different time of day?

Accepted Answer

Consistency matters more than the specific hour. Many clinics suggest late afternoon or evening so that a dose change following a morning INR test can be applied the same day. Pick a time you will reliably keep to and stay with it.

Question 52

What if I take the wrong day's warfarin dose?

Accepted Answer

Do not try to correct it by adjusting the following day. Record what you actually took and on which date, and tell your clinic — particularly if the difference was large or it happened more than once. They will decide whether anything needs to change.

Question 53

Can you drink alcohol while taking warfarin?

Accepted Answer

Most people can drink moderately. The important thing is consistency — a steady, modest intake is far easier for your warfarin dose to accommodate than the same amount concentrated into one session. Some people are advised to avoid alcohol entirely, including those with liver disease or unstable INR control.

Question 54

How much alcohol is safe on warfarin?

Accepted Answer

Most services apply standard national limits: in the UK, up to 14 units a week spread over three or more days; in the US, up to one drink daily for women and two for men. Spreading intake matters as much as the total, because binge drinking raises INR sharply even when the weekly amount is modest.

Question 55

Does alcohol raise or lower INR?

Accepted Answer

Both, depending on the pattern. A heavy session raises INR over the following one to three days by competing with warfarin for liver enzymes. Sustained heavy drinking can lower it by inducing those enzymes — until liver damage develops, at which point INR becomes unpredictable.

Question 56

What happens if I binge drink on warfarin?

Accepted Answer

Your INR is likely to rise over the next one to three days, increasing bleeding risk. Alcohol also impairs balance, and a fall while over-anticoagulated is the most common route to a serious bleed. If you have had a heavy session, watch for unusual bleeding and mention it to your clinic at your next test.

Question 57

How accurate are home INR meters?

Accepted Answer

Modern meters such as the CoaguChek range correlate well with laboratory testing and are accurate enough to guide treatment — the same devices are used as point-of-care instruments in clinics. Agreement is closest in the mid-range and can widen above roughly 4.5. Most services compare a new meter against a venous draw when you start.

Question 58

Does Medicare cover home INR testing?

Accepted Answer

Medicare covers home INR monitoring for certain indications including mechanical heart valves, chronic atrial fibrillation and venous thromboembolism, subject to training requirements and a cap on testing frequency. Coverage details change, so confirm current terms with your provider and supplier.

Question 59

How often should I test with a home INR meter?

Accepted Answer

Many self-testers test weekly, which is associated with substantially better time in therapeutic range than monthly testing. Your clinic sets your schedule, and funding arrangements may cap how often strips are supplied.

Question 60

Can I adjust my own warfarin dose if I self-test?

Accepted Answer

Only under a formal self-management arrangement with specific training and an agreed protocol from your clinic. Most home testers self-test rather than self-manage: you measure, and your clinic decides any dose change.

Question 61

What should I bring to an anticoagulation appointment?

Accepted Answer

Your INR results with dates, your current dose schedule and weekly total, a record of doses actually taken including any missed, notes on anything that changed — new medicines, illness, diet or alcohol changes — and ideally your time in therapeutic range. A printed or exported copy to leave behind is useful.

Question 62

How do I show my doctor my INR history?

Accepted Answer

A chart of your readings against your target range plus your time in therapeutic range communicates more in seconds than a list does in minutes. Bring the underlying data as well, ideally as a CSV or printout that can go into your record.

Question 63

Can I export my INR data from Coagly?

Accepted Answer

Yes. Full history and CSV export are free for every user, reaching back to your first entry — they are not Pro features. The export includes your INR readings, target ranges, notes and dose history, and opens in any spreadsheet.

Question 64

Can I import my INR history from another app?

Accepted Answer

Yes. Coagly imports INR and dose history from CSV, so you can bring years of existing readings across rather than starting from zero. Your time in therapeutic range is then calculated across your whole history.

Frequently asked questions

The questions we get most

More questions, answered in the guides

Normal INR range chart

Time in therapeutic range

Missed a warfarin dose

INR too high

INR too low

Warfarin foods & vitamin K

PT to INR conversion

How often to test INR

Warfarin & antibiotics

Weekly dose schedule

Alcohol & warfarin

INR self-testing at home

INR history for your doctor

Still tracking your INR on paper?