Seed Starting Date Calculator

It is the average date of the last spring frost for your area, after which freezing nights become unlikely. Local extension services and frost maps publish it by zip or postal code, usually as a date with a probability attached.

It depends on the crop, and the seed packet usually states it. Tomatoes and peppers often want six to eight weeks indoors, brassicas four to six, and many leafy greens only two to four weeks.

Tender warm-season plants can be set back or killed by a late frost. Waiting one to two weeks past the average last frost gives milder nights and warmer soil, which reduces transplant shock.

The indoor date is the frost date minus the weeks-before value times seven days. The transplant date is the frost date plus the weeks-after value times seven days. It is plain calendar arithmetic with no rounding.

Dates are treated as plain calendar dates in UTC, so the same inputs give the same output everywhere. Because frost dates are regional averages, treat every result as guidance rather than a guarantee.

Yes. Some crops such as carrots, beans, and radishes dislike being moved and grow better sown straight into the garden. For those, set weeks before to 0 and use the weeks-after-frost date as your outdoor sowing date.

This tool anchors to a single spring frost date. In frost-free climates you can enter your typical planting date as the frost date and use the offsets to plan around it. Fall planting is not modeled here.

Yes. The math steps through real calendar days, so a February 29 in a leap year and the differing lengths of each month are all counted accurately when the offset crosses them.

Yes. The calculation runs entirely in your browser and nothing you enter is uploaded, so your dates and plans stay on your device.