How Many Migraines a Month Is Chronic? The Two Numbers

Headache on 15 or more days a month, for longer than three months, with at least 8 of those days meeting migraine criteria. Both numbers have to be true at once. That is the ICHD-3 definition of chronic migraine, the classification a neurologist diagnoses from.

Most articles give you the fifteen and stop there. The eight is the one doing the work.

Why there are two numbers

Fifteen headache days counts days on which you had a headache. The classification allows those days to be “migraine-like or tension-type-like”, so a run of ordinary dull headaches counts toward your fifteen.

The second criterion is what stops that being enough on its own. At least eight of those days have to be migraine days specifically: either fulfilling the migraine criteria, or days you believed were migraine at onset and that responded to a triptan or ergot derivative.

So someone with six clear migraine days and twelve nondescript headache days has eighteen headache days a month and does not meet the definition. Someone with nine migraine days and six duller ones does. The totals are close and the diagnosis is not the same.

The four ways people miscount

Counting attacks instead of days. An attack running from Thursday evening to Saturday morning is one attack and three headache days. The criteria count days. Anyone who thinks in attacks tends to under-report substantially.

Leaving out the days that were treated successfully. A day you caught early and got through normally is still a headache day. It counts. This is the commonest source of under-counting, because the days that went well are the days you do not remember.

Leaving out the half days. Waking with it and shaking it off by eleven is a headache day.

Reconstructing the month in the waiting room. Pain compresses memory in both directions. A bad fortnight feels like the whole month, and a good stretch erases the bad days before it. ICHD-3 addresses this directly: characterising frequently recurring headache “generally requires a headache diary to record information on pain and associated symptoms day-by-day for at least one month.”

That is the classification itself describing a diary as part of the diagnostic process rather than an optional extra.

Around half of apparent chronic migraine is something else

This rarely appears in articles about the fifteen-day line, and it is the most consequential thing on this page.

ICHD-3 states that the most common cause of symptoms suggestive of chronic migraine is medication overuse, and that roughly 50% of patients who appear to have chronic migraine revert to an episodic pattern after the overused drug is withdrawn.

The two counts interact almost arithmetically. Medication-overuse headache has its own thresholds: ten days a month for triptans, ergots, opioids and combination painkillers, fifteen for plain analgesics on their own. Somebody treating fifteen headache days a month has very likely crossed one of them.

The classification’s instruction is to record both diagnoses when both are met rather than choosing between them, because there is no way to tell in advance which way it will go after withdrawal. So the day count is not merely a label. It is the number that makes a second, often reversible explanation visible at all.

Chronic is not a life sentence

The label sounds permanent. The data says otherwise.

The largest study to follow people across the line tracked 383 adults with chronic migraine for two years, drawn from a random sample of 24,000. Roughly a quarter remitted to episodic migraine over that period — their day count fell back below the threshold and stayed there.

Two predictors mattered. People at 15 to 19 headache days a month were considerably more likely to remit than people at 25 to 31, and people without allodynia — skin so sensitised during attacks that brushing hair or wearing glasses hurts — did better than people with it.

The first predictor is worth sitting with, because it is about the number this whole page is teaching you to count. Sixteen days and twenty-eight days both read as “chronic”, but they are different positions with different prospects, and a diary is the only way you or a clinician will know which one you’re in — or which direction you’re moving.

The count also opens doors. Fifteen headache days is the threshold on Botox’s licence, and how many migraine days it takes to qualify turns on documented days rather than remembered ones.

A worked month

Here is how the counting plays out on a real calendar.

Say March goes like this: an attack running Tuesday evening to Thursday morning in week one (three headache days, all migraine). A one-day attack in week two, plus two ordinary dull-headache days around a deadline. Week three is clear. Week four brings a two-day attack and another attack on the 30th, plus three more nondescript headache days scattered through the month.

Totals: seven migraine days, five non-migraine headache days — twelve headache days. Under the line, despite what felt like a terrible month.

Now the same month with one more three-day attack and one more dull day: sixteen headache days, ten of them migraine. Over the line on both numbers. The difference between those two months is four days — which is exactly why reconstructing the count from memory in a waiting room doesn’t work, and marking days as they happen does.

What the line is for

Chronic migraine is separated from episodic migraine in the classification for a practical reason that ICHD-3 sets out plainly: once headaches are that frequent or near-continuous, individual episodes stop being distinguishable, and the character of the headache can change from day to day or even within a day.

For you, the consequence is that “how many days a month” is among the first questions a neurologist asks, and the answer routes everything after it. It is also the number that later treatment gets judged against. A preventive that moves you from eighteen days to eleven has clearly done something, and without a baseline count there is no way to show that it did.

Which side of the line you fall on, and what follows from it, is a clinician’s call. What you can do is turn up with the count rather than an impression, which is also where the standard disability scores fit in. The same count is what moves a referral along in the first place: getting referred to a headache specialist turns on documented frequency and what has already been tried, rather than on how bad the worst one was.

How to count it without guessing

One month is the minimum ICHD-3 asks for. Three is better, since the definition is about a pattern sustained beyond three months.

Every day gets one mark, including the clear ones:

• Headache today? Yes or no
• Was it migraine? Yes, no, or unsure
• Any acute medication? Which one

Three fields, and both numbers fall out of the columns at the end of the month with no recall involved. The free printable diary is laid out as a monthly grid for this, and a wall calendar with two letters per day does the job as well.

Migraine Journal keeps the distinct-migraine-days figure for the last thirty days rather than a count of attacks, which is the number the criteria are written in, and counts medication days separately so a day with two doses counts once.

The point of the count is not to give yourself a label. It is that “about ten, I think, but some months are much worse” cannot be acted on, and “seventeen headache days last month, nine of them migraine, painkillers on twelve” can be.

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This is background reading, not medical advice, and counting your own days is not a diagnosis. Chronic migraine and medication-overuse headache are both clinical diagnoses, and drug withdrawal in particular is not something to attempt off a blog post. If your headaches have changed pattern, that is a conversation for your GP or neurologist.