Seed Starting Calculator
without the guesswork.
Seed Starting Backward Calculator — Work backward from the last frost date to plan indoor sowing. Uses a focused calculator with visible assumptions. Inputs stay in your browser.
Work backward from your local last-frost date by the crop's indoor-start lead time.
Context matters.
- Cultivar, transplant tolerance and local microclimates can shift the planting window.
Sources & scope
This page shows the source trail, jurisdiction and review date alongside the result. Always confirm time-sensitive rules with the linked authority.
What to know before using the result.
Which frost date should I enter?
Use a local last-spring-frost date from a nearby weather station or extension service, preferably with a probability level you understand.
What does weeks to start indoors mean?
It is the recommended lead time between indoor sowing and the local last-frost date for that crop or variety.
Can I plant outdoors on the calculated date?
The result is an indoor sowing date. Transplant timing still depends on crop tolerance, soil temperature and current weather.