24 hours, 48 hours or days? What the research says about when a migraine really starts.

Four reliable sources. Four different answers.

The American Migraine Foundation says several hours or days. Cleveland Clinic says up to 24 hours. The headache doctors’ rulebook says 2 to 48. A 2025 trial in Nature Medicine looked at attacks where the headache was expected within 1 to 6.

So which is it?

You have a Monday you cannot explain. The yawning at the sink on Sunday. The light that was too bright on the drive home. The migraine that arrived Monday afternoon as if from nowhere.

It did not come from nowhere. The question is how far back it goes.

How early can a migraine start?

A migraine can start hours before the headache, for some people a day or two, and in some people days. The sources differ because they measure different things.

Here is what each one says:

• **American Migraine Foundation:** the first phase can begin several hours or days before the aura or the headache.
• **Cleveland Clinic** (medically reviewed in 2024): the first phase begins up to 24 hours before the headache.
• **International Classification of Headache Disorders:** a 2024 review in Frontiers in Neurology quotes it as defining the prodrome as symptoms 2 to 48 hours before the attack.
• **Nature Medicine, 2025:** a trial analysis studied attacks where people were confident the headache would follow within 1 to 6 hours.

Why the sources disagree

Our read, from the sources themselves, is that they are not counting the same thing.

A definition has to draw a line somewhere, so the headache classification draws it at 48 hours. That is a ceiling researchers use to count the same thing. It is not a promise that every attack starts two days early.

A trial has to enroll people it can study, so the Nature Medicine analysis looked at attacks where people felt sure the headache was close. That is a design choice, not a limit on how early an attack can begin.

And people differ. What feels like the start to one person goes unnoticed by another.

Does a migraine start before the headache?

Yes. A migraine attack is not only the headache.

The American Migraine Foundation describes distinct phases, and the first one, the prodrome, comes before the aura and before the pain. The signs are easy to miss. Yawning. Neck stiffness. A craving. A flat mood. The full list is in what is migraine prodrome.

So the headache is not when the migraine starts. It is when the migraine gets loud.

Migraine phases, with lengths

Two reliable sources give lengths for the four phases of a migraine. They agree on some and differ on others:

• **Prodrome:** the American Migraine Foundation says several hours, sometimes days. Cleveland Clinic says up to 24 hours before the headache.
• **Aura:** both say it can last as little as 5 minutes and as long as 60.
• **Headache:** the American Migraine Foundation says typically several hours up to three days. Cleveland Clinic says 4 to 72 hours.
• **Postdrome:** the American Migraine Foundation says the length varies. Cleveland Clinic says a few hours up to 48 hours.

Put your own diary against that list. It starts at phase three.

How long does a migraine attack last?

Cleveland Clinic says it can take about 8 to 72 hours to go through the four phases of a migraine.

The American Migraine Foundation says the headache phase alone typically lasts from several hours up to three days. The first phase comes before that, and the hangover comes after.

So the attack is longer than the headache. It is easy to count only the part with the pain.

How long does the migraine hangover last?

The last phase is the postdrome. The American Migraine Foundation also calls it the migraine hangover. It lists fatigue, body aches, trouble concentrating, dizziness and sensitivity to light.

Cleveland Clinic says the postdrome usually lasts a few hours up to 48 hours. The American Migraine Foundation says the length can vary.

That is why the two days after an attack feel gone too. They may be part of the attack.

Migraine starts 48 hours before the headache: where that number comes from

You may have seen it written that a migraine starts 48 hours before the headache.

The number has a real source. It is the outer edge of the formal definition of the prodrome, as quoted in the 2024 Frontiers review. It is a boundary the definition uses, not an average.

Other sources put the start closer to the headache. Cleveland Clinic says up to 24 hours, and the Nature Medicine analysis looked at the last 1 to 6. That is why we write that a migraine can start as early as 48 hours before, and why the honest answer to the question in the headline is a range.

Questions

How early can a migraine start?

Sources differ. The American Migraine Foundation says several hours or days before the headache. Cleveland Clinic says up to 24 hours. The formal headache classification uses 2 to 48 hours.

Can a migraine start 48 hours before the headache?

According to the formal definition of the prodrome, yes. It describes symptoms 2 to 48 hours before the attack. It is the outer edge of that definition, and many attacks start closer to the headache.

Does a migraine start before the headache?

Yes. The first phase, the prodrome, comes before the aura and the headache. Its signs include yawning, neck stiffness, food cravings, mood changes and sensitivity to light.

How long does a migraine attack last?

Cleveland Clinic says about 8 to 72 hours to go through the four phases. The American Migraine Foundation says the headache phase alone typically lasts several hours up to three days.

How long does the migraine hangover last?

Cleveland Clinic says a few hours up to 48 hours. The American Migraine Foundation says the length varies.

What are the four phases of a migraine?

The prodrome, the aura, the headache and the postdrome.

Where the line comes in

If a migraine can start hours or days before the pain, the real question is how close your brain was to the edge when the day began.

There is a name for that edge. The Migraine Tipping Line™.

Read what the Migraine Tipping Line™ is, and why your diary never found it →