Frost Date Calculator
Enter a US ZIP code to see the average last spring frost, the first fall frost, and how long your frost-free growing season is. Every date comes with the odds attached, because a frost date is a probability, not a promise.
- NOAA 1991-2020 normals
- By ZIP code
- Odds included
- Free
Frost dates for your ZIP code
32°F is the usual definition
The chance of a frost outside these dates
How frost dates work
They are averages, not deadlines
A "last frost date" of 23 April means half the years have their last frost after that date. Plant tender crops on the average date and you are taking a coin flip. Use the cautious setting for a date only one year in ten beats.
The odds run backwards from what you expect
A more cautious spring setting gives you a LATER date, because you are waiting for the risk of frost to drop. In fall it is the other way round: being cautious means an EARLIER first-frost date.
Your garden is not the weather station
Cold air pools in low spots and drains off slopes, and cities stay warmer than the countryside. A valley bottom can frost a fortnight later in spring than a hill a mile away. The station distance and elevation are shown so you can judge.
Questions people ask
What is my last frost date?
Enter your ZIP code above. You will get the average last spring frost for the nearest NOAA weather station, plus the more cautious date that only one year in ten beats. For most of the US the average falls between mid-March and late May.
When is it safe to plant tomatoes?
Tomatoes, peppers, basil and squash are killed by frost, so wait until the cautious date above has passed, and ideally a week or two beyond it — they also sulk in cold soil. Hardy things like peas, spinach, kale and onions can go out weeks before the last frost.
Where does this data come from?
The frost statistics are the NOAA National Centers for Environmental Information 1991-2020 US Climate Normals, built from 30 years of daily records at each station; we use the 7,129 stations with usable frost figures. ZIP code locations come from the US Census ZCTA Gazetteer, topped up with <a href="https://www.geonames.org/" rel="noopener">GeoNames</a> (CC BY 4.0) for the roughly 8,000 PO-Box-only ZIP codes the Census does not map. The NOAA and Census data are public domain.
Why does the date change when I change the temperature?
Because "frost" is not one thing. A light frost at 36°F nips basil; a hard freeze at 28°F kills tomatoes outright and damages fruit buds. The colder the threshold, the earlier it stops happening in spring, so the date moves earlier.
Does this work outside the United States?
Not yet. NOAA publishes ready-made frost statistics for US stations only; there is no equivalent global dataset, so a worldwide version has to be computed from raw daily temperatures. Canada, the UK and Australia are the likely next additions.
Is climate change making these dates wrong?
These are the 1991-2020 normals, so they already include recent warming — and last frosts have been trending earlier in much of the US. They are updated once a decade, so late in a decade they run slightly conservative. A normal is a 30-year average, not a forecast for this year.
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