Seed Starting Date Calculator
Wondering when to start seeds indoors? Our free seed starting date calculator turns your last frost date and your crop into an indoor sowing window and a transplant date — plus a full reference table so you can plan your whole spring seed-starting schedule at a glance.
Enter your details
The date after which frost is unlikely in your area. Check your local cooperative extension or the Farmer's Almanac for your location.
Your results
| Crop | Sow indoors | Weeks before frost |
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Guideline ranges, not guarantees: frost dates are historical averages, and microclimates vary. Confirm your frost date with a local cooperative extension or the Farmer's Almanac, and treat these dates as a planning starting point.
How to use this calculator
Enter your last frost date — the date in spring after which a freeze is historically unlikely in your area. If you don't know it, check your local cooperative extension office or the Farmer's Almanac frost-date tables for your location. Then pick a crop from the list and your indoor sowing window and transplant date appear instantly.
The sowing window is a date range, not a single day: sow at the start of the window for a longer indoor season, or toward the end if your setup is small or your light is limited. The reference table below the results plans every crop at once, so you can stagger sowings across the season.
How it works
Each crop needs a typical number of weeks indoors before it can go outside. The calculator counts backward from your last frost date: sow-window start = last frost date − max weeks × 7 days, and sow-window end = last frost date − min weeks × 7 days. The transplant date equals your last frost date, when frost danger has passed — always move seedlings outside only after temperatures stay reliably above freezing.
These are typical guideline ranges, not guarantees. Frost dates are historical averages — some years the last freeze arrives earlier or later — and results vary with variety, indoor light, and your local microclimate. A few crops (cucumbers, zucchini/squash, watermelon) actually prefer direct sowing into warm soil and dislike transplanting; they're flagged in the table below.
Frequently asked questions
What is a last frost date?
Your last frost date is the date in spring after which frost is historically unlikely in your area. It's a historical average, not a guarantee — some years the last freeze arrives earlier, some years later. Seed-starting schedules count backward from it: if a crop needs 6–8 weeks indoors before the last frost, you sow it 6–8 weeks before that date.
How do I find my area's last frost date?
Check your local cooperative extension office, the Farmer's Almanac frost-date tables, or your country's weather service records, which publish historical frost dates by location. Because these dates are averages, confirm with a local source — nearby elevation, water, and microclimates can shift them by a week or more.
What happens if I start seeds too early?
Seedlings started too early often become leggy — tall and weak from stretching toward light — and can get root-bound in small pots, which sets them back more than starting later would. They may also outgrow your indoor space or lights before it's warm enough to transplant. When in doubt, sow toward the later end of the window.
Should I start seeds indoors or direct sow them?
Crops with long growing seasons — tomatoes, peppers, eggplant, broccoli, and onions — benefit most from an indoor head start. But cucumbers, squash, zucchini, and watermelon resent transplanting and prefer direct sowing into warm soil (you can start them indoors 3–4 weeks early if you transplant them very carefully). Lettuce, basil, and marigolds do well either way.
What is hardening off and why does it matter?
Hardening off is gradually acclimating indoor seedlings to outdoor sun, wind, and temperature over 7–10 days before transplanting. Start with a few hours of shade and increase exposure daily. Seedlings moved straight from a windowsill to the garden can suffer sunscald and transplant shock, so plan to begin hardening off about a week before your transplant date.