Growing Season Calculator
Work out the length of your growing season from the last spring frost to the first autumn frost.
Formula and sources updated · Data sources · 1View algorithm, constants and default inputs (JSON)
Results
About this calculator
Estimate a frost-free window from the dates you enter. Crop lead times are rough planning buffers, not local forecasts; microclimates and actual frost can differ. Check local forecasts and seed-packet days to maturity before planting.
Worked example
calculated with the default values below
Last frost in spring 2027-05-31 · First frost in autumn 2027-10-31 · What you are growing Warm-season crops Growing season 153 days · Growing season 21.9 weeks · Growing season 5.0 months · Safe planting window 139 days · Latest safe harvest date 2027-10-17 · Suitable crop types Nearly everything, including heat lovers · Frost-free Dates in order
Method and assumptions
D = t₁ − t₀; W = max(0, D − L); t_d = t₁ − L Requires a valid spring date earlier than the autumn date. Crop lead times are rough planning assumptions, not a local frost forecast. Estimate a frost-free window from the dates you enter. Crop lead times are rough planning buffers, not local forecasts; microclimates and actual frost can differ. Check local forecasts and seed-packet days to maturity before planting. Use the cited guidance and your own measurements, bills or product specifications to choose inputs. Sample defaults are not current local data.
Data sources
Use the cited guidance and your own measurements, bills or product specifications to choose inputs. Sample defaults are not current local data.
Disclaimer
These calculators give general estimates. Sizing, pricing, availability and standards vary by brand, retailer and country, so treat the output as a starting point and confirm it against the seller's or authority's own figures.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
D = t₁ − t₀; W = max(0, D − L); t_d = t₁ − L
- t_0
- Last spring frost date
- t_1
- First autumn frost date
- D
- Frost-free days
- L
- Transplant lead time, days
- W
- Planting window, days
- t_d
- Latest safe harvest date
Requires a valid spring date earlier than the autumn date. Crop lead times are rough planning assumptions, not a local frost forecast.
Frequently asked questions
Why does the safe planting window shift with the crop type I select?
Crop buffers are rough planning assumptions, not a local forecast or guarantee. Check local frost forecasts and seed-packet maturity guidance.
Why must the spring frost date come before the autumn frost date?
The calculator measures one frost-free interval from the last spring frost to the first autumn frost. It rejects reversed, impossible, or malformed dates so it does not report a plausible-looking but incorrect harvest deadline. Crop lead times are rough planning assumptions, not a local forecast.
Which inputs and limits apply to Growing Season Calculator?
Use the units shown beside each field. These are form limits, not recommended settings. D = t₁ − t₀; W = max(0, D − L); t_d = t₁ − L Requires a valid spring date earlier than the autumn date. Crop lead times are rough planning assumptions, not a local frost forecast. Estimate a frost-free window from the dates you enter. Crop lead times are rough planning buffers, not local forecasts; microclimates and actual frost can differ. Check local forecasts and seed-packet days to maturity before planting. Use the cited guidance and your own measurements, bills or product specifications to choose inputs. Sample defaults are not current local data.
What is a complete worked example for Last frost in spring = 2027-05-12; First frost in autumn = 2027-10-12?
Inputs: Last frost in spring = 2027-05-12; First frost in autumn = 2027-10-12; What you are growing = Warm-season crops. Calculation: D = t₁ − t₀; W = max(0, D − L); t_d = t₁ − L. Results: Growing season = 153 days; Growing season = 21.9 weeks; Growing season = 5.0 months; Safe planting window = 139 days; Latest safe harvest date = 2027-09-28; Suitable crop types = Nearly everything, including heat lovers; Frost-free = Dates in order. Reference date: 2026-10-12 (UTC).