Seed Starting Date Calculator (From Last Frost)
Enter your average last frost date and the weeks from the seed packet.
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Seed Starting Date Calculator (From Last Frost) by TheCalcTools
How the Seed Starting Date Calculator (From Last Frost) works
Seed packets say how many weeks before the last frost to start seeds indoors (tomatoes and peppers often 6 to 10 weeks) and when it is safe to plant out (warm crops 1 to 3 weeks after the last frost).
Find your average last frost date from your local extension service or meteorological office. It is an average, so protect tender plants if a late frost is forecast.
The formula
Worked example
Using the default values shown in the calculator:
| Average last spring frost date | 2027-04-15 |
|---|---|
| Start indoors: weeks before last frost | 8 |
| Transplant outside: weeks after last frost (negative = before) | 2 |
| Days to maturity after transplant | 70 |
- With a last frost of 15 April 2027, sow tomatoes indoors on Thursday, 18 February 2027.
- Transplant on Thursday, 29 April 2027; first harvest around 8 July 2027.
Result:
| Sow indoors on | Thursday, 18 February 2027 |
|---|---|
| Transplant on | Thursday, 29 April 2027 |
| First harvest around | 8 July 2027 |
| Weeks indoors | 10 |
Frequently asked questions
What if I start too early?
Seedlings get leggy and root-bound. Start later rather than earlier if unsure.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.