What counts as a migraine day: the definition clinicians and insurers use
A migraine day has a precise clinical definition. Here's the rule, six worked examples, and why the count shapes CGRP approval and disability files.
What counts as a migraine day?
A migraine day is any calendar day, midnight to midnight, on which a migraine headache started, continued, or came back. The headache has to look like migraine under the International Classification of Headache Disorders (ICHD-3): at least two of one-sided, pulsating, moderate or severe, or made worse by routine activity, plus either nausea or vomiting, or sensitivity to both light and sound.
Clinical trials add two conventions on top of that. A minimum duration, and a rule that a headache you treated with a triptan counts even if the drug stopped it early.
That's the definition sitting behind your neurologist's chart, your insurer's prior-auth form and the trial data for every CGRP drug. A tracker that just counts "headache logged" is using a different one. So the number on your phone and the number on your chart can drift apart without anyone noticing.
Headache days, migraine days, and the midnight rule
Three rules do most of the counting.
Calendar days, not attacks. An attack that starts at 10 p.m. and lifts at 9 a.m. is one attack and two migraine days. A full 72-hour attack can touch four calendar days. Attacks per month and migraine days per month are different numbers, and the second is the one prescribers and trials report.
Headache days are the bigger bucket. Any day with a headache of any type is a headache day. A migraine day is a headache day that also meets the migraine criteria. The ICHD-3 diagnosis of chronic migraine uses both counts at once: 15 or more headache days a month for more than three months, with at least 8 of those days having migraine features (or believed by the patient to be migraine at onset and relieved by a triptan or ergot).
Treatment can qualify a day. If you know the onset and take a triptan before the full picture develops, most trial protocols still count that day. Which is fair. Treating early shouldn't erase the attack from the record.
One more count runs in parallel: days you took acute medication. That number matters on its own, because frequent triptan use over months is how medication-overuse headache gets diagnosed.
4 to 72 h
duration of an untreated or unsuccessfully treated migraine attackICHD-3, 2018
15+
headache days a month, for more than 3 months, for a chronic migraine diagnosisICHD-3, 2018
8+
of those days meeting migraine criteriaICHD-3, 2018
10+
days a month of triptan use, for more than 3 months, in the triptan-overuse headache criteriaICHD-3, 2018
The trial definition of a migraine day
The International Headache Society's guidelines for preventive-treatment trials define a migraine day by whether a qualified migraine headache begins, continues, or comes back on that calendar day. A headache qualifies when it lasts long enough and has the features of migraine described in the ICHD-3 criteria. Treating it with a migraine-specific medication can also make it count.
Worked examples: which days count
The rule gets clearer the moment you run real days through it. Six common ones are below. The two that trip people up most are the attack that crosses midnight (it counts twice) and the day after an attack when there's no headache at all (it doesn't count, though it's still a lost day).
What happened
Headache day?
Migraine day?
Why
Throbbing left-sided headache, 6 hours, nausea, had to lie down
Yes
Yes
Meets ICHD-3 pain features and associated symptoms
Attack starts 10 p.m. Tuesday, still there on waking Wednesday
Yes, both days
Yes, both days
Onset day and continuation day each count
Dull pressure on both sides, 3 hours, no nausea, light didn't bother you
Yes
No
Tension-type-like; misses migraine features
Familiar migraine onset, triptan at 20 minutes, gone in an hour
Yes
Usually yes
Trial convention counts triptan-treated headaches
No headache. Brain fog, neck stiffness, wiped out the day after an attack
No
No
Postdrome symptoms alone don't meet headache criteria; log them separately
Attack Monday, clear Tuesday, back Wednesday afternoon
Mon and Wed
Mon and Wed
Each day with a qualifying headache counts; the clear day doesn't
Applies ICHD-3 criteria for migraine without aura and the clinical-trial calendar-day convention. Your clinician's diagnosis governs your own record.
Why the count matters for CGRP approval and disability
Prior-authorization requests for CGRP monoclonal antibodies usually ask for a documented number of monthly migraine days, alongside the preventives you've already tried. Thresholds differ by plan. Reviewers read the number literally.
That cuts both ways. A diary that folds tension-type days into migraine days can get questioned. And a diary that quietly drops the second day of a midnight-crossing attack undercounts you, sometimes enough to land below a plan's cutoff.
Disability files run on the same logic. In the US, the Social Security Administration evaluates primary headache disorders under Social Security Ruling 19-4p, which looks for a detailed description of a typical headache event from an acceptable medical source. A clean, criteria-based day count is the spine that description hangs on.
Don't pad the count
Logging a postdrome day or a mild tension-type day as a migraine day can feel like it strengthens your case. It usually backfires. A reviewer who spots days that don't meet criteria can discount the whole diary. Keep migraine days honest, and document the other bad days in their own column.
Where postdrome days belong
The definition leaves a gap, and plenty of you live in it. The day after a bad attack, with no headache but a brain too slow to hold a sentence and light that still feels sharp, isn't a migraine day under any criteria above. It's still a day you didn't work.
So track it as its own thing. Postdrome records the after-phase as a separate phase on the same timeline as the headache. Your migraine-day count stays clean for the prior-auth form, and the hours of fog and fatigue afterward stay visible for the neurologist conversation and the disability file. The record lives on your device, it's yours to export, and it's a one-time lifetime price.
When a headache day needs more than a log
Some headaches shouldn't wait for the monthly count. Get urgent care for a sudden, severe headache that peaks within about a minute, a headache with fever and a stiff neck, or one with new weakness, numbness, slurred speech or confusion.
Book a sooner appointment if your pattern changes: a new kind of headache after 50, attacks getting clearly more frequent, aura that runs past an hour or looks unlike your usual, or acute medication creeping up toward most days of the month.
Keep a migraine-day count that matches your chart, and a record of the days after.
Every count in this piece comes from the ICHD-3 criteria and the clinical-trial calendar-day convention, the same rules behind CGRP prior-auth reviews and neurologist charts. Postdrome keeps those migraine days separate from the after-phase, so the number you report holds up and the fog that follows still gets recorded.
