Growing Season Days Calculator
Knowing your frost-free growing season length is essential for matching crop varieties to your climate. A crop that needs 90 days to mature will not ripen before the first fall frost in a location with only 80 frost-free days. This calculator subtracts the last spring frost date from the first fall frost date to give the total number of frost-free growing days. It also tells you the latest safe planting date for a crop with a given days-to-maturity, accounting for a buffer of 1 week before the first fall frost. Enter your frost dates from NOAA or USDA extension sources.
Growing season formula
Frost-free days = First fall frost date - Last spring frost date
Latest planting date = First fall frost date - Crop days-to-maturity - 7 days buffer
The 7-day buffer gives a margin for slower-than-expected maturity. Increase to 14 days for crops that must fully ripen before frost (tomatoes, squash).
Typical growing season by US region
- Northern New England, High Plains: 100 to 130 frost-free days.
- Midwest, Mid-Atlantic: 150 to 180 frost-free days.
- Pacific Northwest coast, Southeast: 200 to 260 frost-free days.
- Gulf Coast, Southern California: 270 to 365+ frost-free days.
- Find your exact dates from NOAA Climate Data Online (climate.weather.gov).
Growing season calculator: frequently asked questions
How do I find my frost dates?
The USDA Plant Hardiness Zone Map and NOAA Climate Data Online provide historical first and last frost dates by location. Your local Cooperative Extension office also publishes frost date tables specific to your county.
What does days-to-maturity mean on a seed packet?
Days-to-maturity is the number of days from transplanting (for starts) or direct seeding (for direct-seeded crops) until the crop is ready to harvest. Compare this number to your frost-free window to determine if a crop will mature before the first fall frost.
Can I grow crops with longer maturity than my frost-free season?
Sometimes. Use season extension tools like frost cloth, cold frames, or row covers to protect crops before the last frost in spring or after the first frost in fall. These can extend your effective growing season by 4 to 8 weeks.
What is the growing season in the continental US?
Growing seasons range from fewer than 100 days in high-elevation Rocky Mountain valleys to over 300 days in coastal Florida and Southern California. Most of the Midwest has 150 to 180 frost-free days. The USDA publishes regional averages.
How do I account for the 50 percent frost probability date?
Standard frost dates are based on the date when there is a 50 percent chance of frost. For spring planting, wait until after this date for tender crops. For extra safety, use the 10 percent probability date (later in spring, earlier in fall), also available from NOAA.
Official sources
- NOAA Climate Data Online, frost date normals: ncdc.noaa.gov.
- USDA Plant Hardiness Zone Map: planthardiness.ars.usda.gov.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.