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Seed Starting Calculator

Enter your last frost date and your crop. We'll count backward and tell you exactly when to start seeds indoors and when to plant out.

Don't know yours? Search "average last frost date" plus your town or zip code — most extension services and weather sites publish it.

How it works

Seed packets say things like "start indoors 6–8 weeks before your last frost." This calculator just does that math for you. Pick a crop and enter your average last spring frost date, and it projects:

  • Indoor sowing window. The range of dates to start seeds inside, based on published university-extension timing for each crop.
  • Transplant window. When those seedlings should go into the garden. Hardy crops go out before the frost date; tender crops wait until after it.

Frost dates are averages, not guarantees — roughly half of years see a frost after the "last frost date." Watch your forecast in the week around transplant time, and harden seedlings off with a few days of increasing outdoor exposure before they move out for good.

Starting too early is the most common seed-starting mistake — leggy, root-bound transplants usually end up behind plants started on time. We learned that the hard way: read what happened when we started tomatoes six weeks too soon. Once your seedlings are in the ground, our days-to-harvest calculator picks up where this one leaves off.