Seed Starting Date Calculator
Count back from your last frost date to find when to start seeds indoors and when to transplant them outside.
How it works
Sow date = last frost − (weeks before × 7 days) · Transplant date = last frost + (weeks after × 7 days)
Most seed packets give a head-start window such as "start 6–8 weeks before last frost." Counting back that many weeks from your local last-frost date gives the indoor sowing date; adding a hardening-off buffer after the frost gives a safe transplant date. Tender crops (tomatoes, peppers, basil) want warm soil and are set out a week or two after frost, while hardy crops can go out on or before the frost date.
Worked example
With a last frost of April 15 and a packet that says start 6 weeks early: April 15 − 42 days = March 4 to sow indoors. Setting plants out 1 week after frost gives a transplant date of April 22.
Frequently asked questions
How do I find my last frost date?
Look up the average last spring frost for your ZIP code or region from a local extension office or a frost-date database. It is an average, so late cold snaps are still possible — the buffer weeks after frost help protect tender seedlings.
Which seeds should I start indoors?
Slow-growing, heat-loving crops benefit most: tomatoes, peppers, eggplant, and many herbs and flowers. Fast growers and root crops (beans, squash, carrots, radish) are usually direct-sown outside instead.
What does "hardening off" mean?
It is the week or so of gradually exposing indoor-grown seedlings to outdoor sun and wind before transplanting, so they are not shocked. Build it into the gap between your last-frost and transplant dates.
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This calculator is for educational purposes. Double-check important results before acting on them.