Frost Date Planting Calculator
Enter your last spring frost date and a crop to get when to start seeds indoors and when it is safe to plant outside.
How it works
Outdoor date = last frost + crop offset weeks · Indoor start = last frost − head-start weeks
Almost every planting date is anchored to your average last spring frost. Tender, heat-loving crops like tomatoes, peppers and squash go out only after that date has passed and the soil has warmed, and many are started indoors weeks earlier to gain a head start. Cool-season crops like lettuce are the exception — they can be direct-sown weeks before the last frost because light frost does not harm them. The last frost is an average, so watch the forecast and be ready to protect seedlings from a late cold snap.
Worked example
With a last frost of April 15, tomatoes are transplanted about 1 week after — around April 22 — and their seeds are started indoors about 7 weeks before the frost, near February 25. Lettuce, by contrast, is direct-sown around March 18, four weeks before the frost.
Frequently asked questions
What is a "last frost date" and where do I find mine?
It is the average date of the final overnight freeze in spring for your area, based on decades of local weather records. You can look it up by ZIP or postal code through a national weather service or extension office; it is a probability average, not a guarantee.
Why start some seeds indoors and direct-sow others?
Long-season, heat-loving crops (tomatoes, peppers) need a head start to ripen before fall, so they are sown indoors weeks early and transplanted after frost. Fast or cold-tolerant crops (lettuce, beans, squash) grow quickly outdoors and often resent transplanting, so they are sown directly in the ground.
Can I plant earlier than these dates?
You can gamble on an early planting if the forecast looks mild, but a late frost can kill tender seedlings overnight. Use row covers, cloches or cold frames to protect early plantings, and keep hardier crops as your only truly frost-safe early bets.
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This calculator is for educational purposes. Double-check important results before acting on them.