Allergy Season Calculator

Pick a US region and a month, and this returns the pollen risk you should expect, which plant is doing the damage, and what to do about it. It is a seasonal expectation, not a forecast: it will not know that this particular April is running two weeks early because of a warm March. For today’s actual grain count, check the National Allergy Bureau station nearest you. Use this to decide when to start medication, when to book the hiking trip, and which month to avoid moving house.

What the risk levels mean

Each region carries a 1 to 5 score for every month, drawn from typical bloom calendars.

The five regional calendars

• Northeast: quiet from November through February. Tree pollen climbs in March and peaks in April, May is the worst month because tree and grass overlap, then grass carries June. Ragweed starts in August and peaks in September.
• Southeast: the longest season in the country. Juniper and early trees are already going in January, oak and pine run March through April, grass peaks in May, and ragweed peaks in September. Only December is genuinely quiet, and November brings mold instead.
• Midwest: similar spring to the Northeast, but the autumn is worse. Ragweed peaks in August and stays high through September, which is the annual low point for a lot of people in Ohio, Illinois and Iowa.
• Southwest: the odd one out, and the reason a single national calendar does not work. Mountain cedar, properly Juniperus ashei, pollinates in the dead of winter. December through February is cedar fever season in central Texas, and it is the only place in the US where the worst month can be January. Summer is the quiet half of the year here.
• Pacific Northwest: alder in February, tree pollen peaking in April, then a heavy grass season in May and June. The autumn threat is mold rather than pollen, once the rain returns in September.

Pollen counts do not share one scale

If you look up a count in grains per cubic meter, the number only means something next to its own pollen type. The National Allergy Bureau thresholds:

A grass count of 30 is a bad day. A tree count of 30 is barely worth a tablet. Any site that gives you one universal 0 to 200 scale is quietly averaging three different things.

Timing, which matters more than dose

Most pollen is released in the early morning, and airborne counts usually peak mid-morning, with grass often producing a second rise on warm afternoons. Ragweed is an early riser: 6 to 11 AM.

Oral antihistamines need roughly 1 to 2 hours to reach useful blood levels, so take one before you go out rather than after the sneezing starts. Nasal corticosteroids such as fluticasone or triamcinolone work on a completely different clock: they need 2 to 4 weeks of daily use before they reach full effect. That is the single most common mistake people make with them. If April is your bad month, you start the nasal spray in mid-March, not on the first bad morning.

The rest of it

Rain washes pollen out of the air, then a dry windy day after rain is often the worst of the season. Shower and change clothes when you come in, because the pollen rides home in your hair and onto the pillow. Wraparound sunglasses genuinely help with eye symptoms. And keep the car windows up with recirculate on: a car with the vents open is a pollen collector with seats.