Plan your garden with the Seed Starting Date Calculator. Enter your last frost date and select a crop type to find out exactly when to start seeds indoors and when to transplant outdoors. You'll get a personalized planting window so your seedlings are ready at the right time — no guesswork, no late starts.
Start Seeds Indoors By
--
Safe Transplant Date Outdoors
--
Weeks Before Frost to Start
--
Days Until You Should Start Indoors
--
Indoor Growing Window
--
Your last frost date is the average date of the final freezing temperature in spring for your location. You can find it by entering your ZIP code on sites like The Old Farmer's Almanac, or by contacting your local cooperative extension office. It's the key date used to count backward for starting seeds indoors.
Many crops need a longer growing season than your local climate naturally provides. Starting seeds indoors gives transplants a head start so they're ready to go in the ground as soon as outdoor conditions are safe. This is especially important for tomatoes, peppers, and eggplant in colder climates.
It depends on the crop. Fast-growing plants like cucumbers and squash need only 3–4 weeks, while slow growers like celery, peppers, and artichokes may need 10–12 weeks. This calculator applies the recommended window for each crop automatically based on your selected plant.
Some crops are frost-tolerant and can go outside 2–4 weeks before your last frost date (like broccoli or cabbage), while tender crops like tomatoes and peppers should wait until 1–2 weeks after the frost date. The transplant offset adjusts the safe outdoor planting date accordingly.
This calculator is designed around spring planting using your last frost date. For fall gardening, you'd use your first fall frost date and count backward from that. Many extension offices and almanac sites provide fall planting calculators that work on the same principle.
Seedlings started too early can become leggy, root-bound, or stressed before transplant time arrives. Overgrown transplants often struggle to establish well outdoors. It's better to follow recommended timing than to start weeks ahead hoping for an earlier harvest.
The general principle is the same — count back from your frost date — but the specific weeks vary by plant. Herbs like parsley and rosemary need a longer indoor head start, while fast-growing flowers like zinnias and marigolds need only a few weeks. This calculator adjusts for each crop category.
Don't panic — most crops have a flexible window of several weeks. If you've missed the earliest start date, you can still begin seeds and simply transplant a bit later. Some fast-maturing crops can even be direct-sown outdoors after your frost date if indoor starting isn't possible.