Seed Starting Calculator
Work backward from the last frost date to plan indoor sowing. Inputs stay in your browser.
Work backward from your local last-frost date by the crop's reviewed indoor-start lead time.
Context matters.
- Cultivar, transplant tolerance, germination temperature, hardening and local microclimates can shift the planting window.
Sources & scope
The calculation guide and this source trail show what the result means, where the rule came from and when it was last reviewed. This is source-and-calculation QA, not a claim of medical, legal, tax or other professional review; time-sensitive decisions still belong with the linked authority.
A visible path from input to answer.
Work backward from the last frost date to plan indoor sowing. The page keeps the calculation scope and its limits beside the result so the output can be checked, copied or revisited.
- Read the record. The calculator uses Local last frost date, Crop or variety, Starting method and Weeks before last frost supplied in the form.
- Apply the scope. It applies the User-provided values — verify local or contractual assumptions reference and the explicit date, unit and counting conventions shown in the result.
- Expose the checkpoints. Intermediate rows, warnings and timeline events stay visible; the emphasized row identifies the primary checkpoint when one exists.
Work backward from your local last-frost date by the crop's reviewed indoor-start lead time.
- Start seeds indoorsMar 19, 2026
Calculation purpose: Work backward from the last frost date to plan indoor sowing. This is a general planning reference; local conditions, product instructions or personal records can override the estimate.
Calendar inputs use plain year-month-day semantics. Leap days, month ends, date-pair order and unsupported dates are checked before the result is shown.
Rule set 1.1.0 · Last reviewed 2026-08-20 · Next review due 2027-02-20. The source panel below contains the linked evidence.
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.