Seed Starting Date Calculator
Counting Backward From the Last Frost
Seed packets almost always give their indoor-starting instructions relative to the last frost date, not a calendar date — "start 6-8 weeks before last frost" means something different in a zone that clears frost in April versus one that doesn't clear until June. This calculator does the subtraction for you once you know your local last-frost date.
The Formula
Typical Lead Times by Crop
The right number of weeks before transplant depends on how slowly a crop germinates and how much of a head start it needs indoors:
| Crop | Weeks Before Last Frost |
|---|---|
| Peppers, eggplant | 8–10 weeks |
| Tomatoes | 6–8 weeks |
| Broccoli, cabbage, kale | 6–8 weeks |
| Lettuce, other greens | 4–6 weeks |
| Cucumbers, squash, melons | 3–4 weeks |
Always confirm against the specific seed packet — lead time varies by variety, not just crop type.
Why the Last-Frost Anchor Matters
- Avoiding leggy seedlings — starting too early produces overgrown, root-bound transplants by the time it's safe to move them outside.
- Avoiding a late start — starting too late means transplants go in the ground undersized, delaying the harvest window.
- Succession sowing — once the base date is known, gardeners can offset it by a week or two at a time to stagger harvests of fast-maturing crops like lettuce.
How to Use This Calculator
- Enter your area's average last frost date.
- Enter how many weeks before transplant the seed should be started (defaults to 6, typical for many common crops).
- Select Calculate to get the exact date to start seeds indoors.
Related Calculations
Once seedlings are ready, work out how many will fit in the bed with the Plant Spacing Calculator, or check which crops pair well together using the Companion Planting Calculator.