About this tool
Seed Starting Date Calculator is a free, in-browser tool that turns your last spring frost date into a personal sowing schedule. Enter the frost date and pick a crop, and it returns the date to start seeds indoors and the date to transplant seedlings outside, along with how many weeks before frost you sow. Frost dates are entered by you — the tool does not fetch weather data. Nothing is uploaded; the math runs on your device.
Each crop carries a recommended number of weeks to sow before the last frost and a transplant offset in weeks relative to frost. The indoor sow date = frost date − weeks-before × 7 days, and the transplant date = frost date + offset × 7 days, where a negative offset means transplant before the frost date for cold-hardy crops. All date arithmetic uses Date.UTC-based day counting, so results never shift by a day around daylight-saving changes.
Use it to plan a whole season: look up your region's average last spring frost from a local extension service or frost-date map, enter it once, and step through each crop. Tender crops like tomatoes, peppers and basil transplant after frost, while cool-season crops like lettuce and broccoli go out a couple of weeks before it.