Frost Date Calculator

An "average last frost date" is not a guarantee. NOAA calculates freeze dates from the 1991 to 2020 climate normals as probabilities: the median (50%) last spring freeze is the date after which frost still happens in half of years. If your median last frost is April 15, planting frost-tender tomatoes on April 15 is a coin flip.

NOAA also publishes 10% and 90% dates. The 10% spring date is the one after which a freeze occurs in only 1 year out of 10, and at most stations it falls roughly two weeks after the median. This calculator applies that typical 14-day spread, so a cautious plan moves an April 15 median to April 29 in spring and an October 15 median to October 1 in fall.

The frost-free season is the number of days between the last spring freeze and the first fall freeze. April 15 to October 15 spans 183 days on the calendar, leaving 182 frost-free days once both freeze dates are excluded. At the cautious 10% level the same location has only 154 days, which matters when you compare it with seed packet days to maturity.

• A 75-day sweet corn or a 70-day tomato fits easily in 150 days.
• Long-season crops such as sweet potatoes (90 to 120 days from transplant) and winter squash need planning in short-season areas.
• Days to maturity for transplanted crops count from transplanting, not from sowing seed indoors.