Seed Starting Calculator

How it works

Sow indoors = last frost date − (weeks before × 7 days) · Transplant = last frost date + (weeks after × 7 days)

Seed packets time everything relative to your local last spring frost — the date after which a hard freeze is unlikely. Tender crops are started indoors a set number of weeks before that date so they are stout seedlings by the time it is safe to plant out, and they go into the garden a week or two after the last frost once the soil has warmed. This calculator counts backward from the frost date to your sowing day and forward to your transplant day. The right number of weeks varies by crop: tomatoes and peppers typically want six to eight weeks of a head start, while fast growers like cucumbers need only two to three, and hardy greens can skip the indoor stage entirely.

Worked example

With a last frost date of April 15, 2026 and a crop that wants a 6-week indoor head start: sow indoors 6 × 7 = 42 days earlier, on March 4, 2026. Transplanting 2 weeks after the last frost puts the seedlings out around April 29, 2026 — 42 days from sowing to the frost date.

Frequently asked questions