Frost Date Calculator

Planting schedules live or die by frost timing, and this tool estimates the average first and last frost dates for your location using your USDA Plant Hardiness Zone. Those two dates frame the growing season: the average last spring frost tells you when tender annuals can go in the ground with reasonable confidence, while the average first fall frost marks the deadline for harvesting frost-sensitive vegetables before cold damage sets in.

The dates come from a built-in table with one estimated last-spring and first-fall frost date for each whole zone from 3 to 10. The calculator does not look up weather-station records, does not split zones into a and b halves, and does not attach a probability to either date. The growing season is the count of days between the two dates, from 123 days in zone 3 to 350 in zone 10. For dates tied to a real place, NOAA's 1991–2020 U.S. Climate Normals give spring and fall 32°F freeze dates at probability levels from 10% to 90% for individual weather stations, and NOAA's normals map can search them by ZIP code.

Treat the output as a long-run average rather than a guarantee. Microclimates and any given year's weather can push actual frost earlier or later, so leaning on the average last frost date alone leaves you exposed to a late cold snap. It also helps to keep two related ideas separate: the USDA Plant Hardiness Zone describes average minimum winter temperatures, which is not the same thing as the frost dates this calculator returns.