How Many Migraines a Month Is Normal? The 15 Day Line

The question does not have the kind of answer people expect. What headache medicine defines is not an average but a threshold, and it sits at 15 headache days a month. That line, drawn by the International Classification of Headache Disorders, separates episodic migraine from chronic migraine, and where you fall relative to it changes how the condition is classified and how it is studied. Counting your own headache days is how you find out which side of it you are on.

The number that matters is 15, not an average

People asking how many migraines a month is normal are usually asking two things at once: whether their own count is unusual, and whether it is a warning sign. The classification answers the first with a definition rather than a distribution, and the second only by implication.

The International Classification of Headache Disorders, third edition, known as ICHD-3, describes chronic migraine as headache occurring on 15 or more days a month for more than 3 months, which, on at least 8 days a month, has the features of migraine headache. Below that line the classification refers to episodic migraine, and it explains the split by what happens to the attacks themselves.

Two details in that definition carry most of the weight. The 15 days are headache days of any kind: on those days ICHD-3 counts migraine-like and tension-type-like headaches together, though not secondary headaches. The 8 day sub-threshold is what keeps the diagnosis tied to migraine. On at least 8 days a month, for more than 3 months, the headache has to carry the characteristics and associated symptoms the migraine criteria describe, or be a headache the patient believed to be migraine at onset that was relieved by a triptan or ergot derivative.

A history requirement sits underneath both numbers. The criteria apply to a patient who has had at least five attacks fulfilling the relevant criteria for migraine without aura and/or migraine with aura. The diagnosis presupposes a migraine history instead of replacing one.

And a fourth criterion closes the set, which the popular summaries almost always drop. ICHD-3 requires that the headache is not better accounted for by another ICHD-3 diagnosis. That clause is doing more work than it looks like it is doing. It is what keeps the label off headaches with a different cause, and it is not a clause you can apply to yourself, because applying it means having ruled out the other things a headache can be. Everything below is written on the assumption that a clinician has done that.

Why the line was drawn there

ICHD-3 explains its own reasoning, and the explanation is practical rather than statistical. The reason for singling out chronic migraine from episodic types, the classification says, is that it is impossible to distinguish the individual episodes of headache in patients with such frequent or continuous headaches. It adds that the characteristics of the headache may change not only from day to day but even within the same day.

That describes a different clinical problem, not a worse version of the same one. Below the line, headache has edges: an onset, a peak, an end, a recovery you can point to on a calendar. Above it the edges blur, and the question of how many attacks you had stops having a clean answer.

A precedence rule follows from the blurring. Because tension-type-like headache sits inside the criteria for chronic migraine, ICHD-3 states that this diagnosis excludes the diagnosis of tension-type headache or its types. If you meet the chronic migraine criteria, only one label survives. The difference between the two is worth understanding on its own terms, which is why we wrote a separate piece on migraine versus tension headache.

On how common it is, the American Migraine Prevalence and Prevention Study mailed surveys to a sample of 120,000 US households selected to represent the US population. Of the respondents, 11.79% met the migraine criteria then in use and 0.91% met the criteria for chronic migraine, which the authors summarised as a prevalence of nearly 1%. Chronic migraine represented 7.68% of migraine cases overall. Those authors classified chronic migraine with modified Silberstein-Lipton criteria and the second edition of the classification, so the figures sit close to the ICHD-3 wording above without having been produced by it.

That same US study measured disability with the Migraine Disability Assessment Scale and found people with chronic migraine far more likely to fall in the highest grade than people with episodic migraine, 37.96% against 9.50%. That gap is why the 15 day line is more than bookkeeping. We broke down how the MIDAS score is calculated separately.

Below 15, frequency still has rungs

Researchers do not treat everything under 15 days as one group. Writing in Neurology in 2009, Richard Lipton set out the model headache experts use, which envisions transition into and out of four distinct states: no migraine, low-frequency episodic migraine at fewer than 10 headaches per month, high-frequency episodic migraine at 10 to 14 headaches per month, and chronic migraine at 15 or more.

Movement between those states runs in both directions and has been measured. In the same US cohort, 209 of the 8,219 individuals who had episodic migraine in 2005, or 2.5%, had developed transformed migraine, the chronic form as that study defined it, by 2006. Lipton's review put the estimate the same way: population studies put the transition to chronic migraine at about 2.5% per year.

Risk is not spread evenly across everyone. Baseline headache frequency was itself a risk factor in that analysis, and the wider list of associated factors included obesity, stressful life events, snoring, and overuse of certain classes of medication. In the 2008 study by Bigal and colleagues in Headache, people using medications containing barbiturates or opiates were at increased risk relative to acetaminophen users, with odds ratios of 2.06 and 1.98, while use of triptans at baseline was not associated with prospective risk.

None of which makes a high count a verdict. The same review noted that emerging data on the longitudinal risk suggest that, in a population at risk, chronic migraine may be a preventable disorder. Which is the argument for knowing your number while it is still moving.

Medication overuse headache runs on its own calendar

Another reason to count is that treating attacks carries a frequency limit of its own. ICHD-3 defines medication-overuse headache as headache occurring on 15 or more days a month in a patient with a pre-existing primary headache, developing as a consequence of regular overuse of acute or symptomatic headache medication on 10 or more or 15 or more days a month depending on the medication, for more than 3 months. It usually, but not invariably, resolves after the overuse is stopped.

Limits differ by drug class. Ergotamine, triptans, opioids and combination analgesics each carry a threshold of 10 or more days a month for more than 3 months. Non-opioid analgesics carry a threshold of 15 or more days a month for more than 3 months, and ICHD-3 regards all of them as a single class, so paracetamol on some days and an NSAID on others still counts cumulatively.

There is a further category for people who exceed nothing individually but reach a total of 10 or more days a month, for more than 3 months, across ergotamine, triptans, non-opioid analgesics and opioids combined.

Combination analgesics deserve a note, because few people think of them as a category. ICHD-3 uses the term for formulations combining drugs of two or more classes, each with analgesic effect, such as paracetamol and codeine, or acting as adjuvants, such as caffeine. It adds that the most commonly overused combination analgesics combine non-opioid analgesics with opioids, butalbital and/or caffeine. A familiar pharmacy box can sit in that group. The exception matters as much as the rule: a product combining only two non-opioid analgesics, such as acetylsalicylic acid and paracetamol, with no adjuvant, is not counted as a combination analgesic, because for the purposes of ICHD-3 both drugs are in the same class. That box is on the 15 day line, not the 10 day one.

ICHD-3 is candid about where the numbers come from. In the criteria for the various subtypes, it says, the specified numbers of days of medication use considered to constitute overuse are based on expert opinion rather than on formal evidence. They are consensus lines, not experimental results, which makes them prompts for a conversation rather than verdicts.

None of this is a fringe problem. Epidemiological evidence from many countries, ICHD-3 reports, indicates that more than half of people with headache on 15 or more days a month have medication-overuse headache.

Around 50% of patients who appear to have chronic migraine revert to an episodic type after drug withdrawal, the classification notes, and clinical evidence shows the majority of patients with medication-overuse headache improve after discontinuation of the overused medication, as does their responsiveness to preventative treatment. Stopping is a medical decision with real risks, and it belongs with your doctor rather than with an article.

Counting is harder than it looks

Criteria count days, not attacks, and the two are different units. An untreated or unsuccessfully treated migraine attack can last anywhere from 4 to 72 hours, so one attack can cover parts of three dates. Someone who reports four migraines a month may be reporting seven or eight headache days, which lands them somewhere quite different on the scale.

ICHD-3 does not ask anyone to reconstruct this from memory. It says that characterization of frequently recurring headache generally requires a headache diary to record information on pain and associated symptoms day-by-day for at least one month. One month is the floor. The chronic migraine criteria run over three, which is a full quarter of daily entries before the question can be answered at all.

Some tracking apps turn that arithmetic into a by-product of logging rather than a monthly chore. MigrAid, for example, records prodrome, attack and postdrome as separate stages and exports any date range as a PDF or CSV, so the day count you hand over at an appointment comes from what you logged at the time.

One pattern is worth separating out before you draw conclusions from a total. ICHD-3 notes that migraine without aura often has a menstrual relationship, and a cycle-linked pattern can make three months look chaotic when they are not. That pattern has criteria of its own and needs at least three cycles of tracking to see.

When to see a doctor, and when not to wait for one

Start with the part that is not about counting at all. A minority of headache patients have a secondary headache disorder, meaning the headache is a symptom of something else, and a few of those presentations need care the same day. A headache of sudden or abrupt onset is what headache medicine calls a thunderclap headache, defined in ICHD-3 as reaching maximum intensity in under 1 minute, and the SNNOOP10 authors describe it as associated with serious intracranial disorders of vascular origin, in particular subarachnoid hemorrhage. One prospective study they cite identified subarachnoid haemorrhage in 25% of 148 episodes of thunderclap headache. On neurological signs the same paper is blunt: neurologic deficits should always raise serious concern regardless if a headache is present or not.

So there is a category here that has nothing to do with your monthly total. The American Migraine Foundation states it plainly: if you experience any of these symptoms during what otherwise seems like a migraine attack, you should go to the hospital immediately. On thunderclap headache it advises that if you are experiencing this type of headache pain for the first time, you should visit the ED, meaning the emergency department. On neurological symptoms it advises that you should also visit the ED right away if you experience any new and sudden-onset neurological symptoms, including weakness on one side of the face or body, numbness, the inability to speak normally, vision changes, unusual dizziness, or trouble walking. If that is what is happening now, stop reading and get emergency help. Do not book an appointment, do not wait to see whether it settles, and do not wait for a diary to fill up.

The rest of the SNNOOP10 list is appointment material. It enumerates red flags including systemic symptoms such as fever, neoplasm history, neurologic deficit including decreased consciousness, sudden or abrupt onset, older age with onset after 65 years, pattern change or recent onset of new headache, positional headache, headache precipitated by sneezing, coughing or exercise, papilledema, progressive headache and atypical presentations, pregnancy or puerperium, painful eye with autonomic features, posttraumatic onset of headache, pathology of the immune system such as HIV, and painkiller overuse or a new drug at onset of headache. The published age cue is 65, and it is worth adding that a first severe or genuinely new headache later in life is worth showing someone whatever the exact number.

Frequency is not the only thing that decides whether to go. Severe disability was far more common among people with chronic migraine in the prevalence data, but a handful of attacks a month can still take those days away completely. Migraine, as the ID Migraine validation study put it in Neurology in 2003, is a highly prevalent and disabling illness that remains substantially undiagnosed in primary care. Under-counting your own days does nothing to help that.

One item on the SNNOOP10 list matters directly to the question this article is about: pattern change or recent onset of new headache. A rising monthly count is a change in pattern, which makes it a reason to book an appointment instead of waiting to see whether next month is quieter. Bring the medication days too, since a count creeping toward 10 or 15 a month is a specific, countable thing a doctor can act on.

Ask about prevention by name while you are there. Preventive treatment is a different thing from the medicine you take during an attack: it is taken regularly, with the aim of reducing how often attacks arrive. Reviewing the evidence base in Continuum in 2015, Silberstein wrote that migraine preventive drug treatments are underutilized in clinical practice, and that the choice of preventive treatment of migraine should be based on the presence of comorbid and coexistent illness, patient preference, reproductive potential and planning, and best available evidence. Every one of those inputs is personal, which is why this article is not going to name a number that should trigger it. It is a conversation to ask for, with your own count in front of you.

The bottom line

The useful number is not an average but a line, and it sits at 15 headache days a month for more than 3 months, with at least 8 of them carrying migraine features over the same period, in someone with a migraine history, and with no other diagnosis better accounting for the headache. Alongside it sit medication day limits of 10 or 15 depending on the drug class. Everything below that is your own baseline, and the comparison that matters is against your own previous quarter.

Which is the case for writing it down. A number you counted is something you can bring to a doctor, check against last quarter, and act on. A number you estimated is a shrug with a decimal point. And none of it applies to a headache that arrives at full force in under a minute or brings new neurological symptoms with it, which is an emergency and not a data point.