Frost Date Calculator

A tool that turns your last spring frost date and first fall frost date into a growing season length and a set of vegetable seed-starting windows. This calculator does that math directly from dates you enter, rather than guessing a location from a ZIP code, since a wrong station match would hand back a confidently wrong date.

Because a ZIP code does not map cleanly to a single weather station. NOAA publishes 30-year frost normals per station, not per ZIP, and a large or hilly ZIP code can sit closer to several stations at different elevations with genuinely different frost dates. Rather than guess which one applies to you and risk a wrong answer with false confidence, this calculator asks for your own last and first frost dates directly and runs exact arithmetic on them.

NOAA's National Centers for Environmental Information publish 30-year Climate Normals, including frost dates, by weather station, linked directly from this calculator. Your local university extension office is another reliable source and can usually give you a figure calibrated to your specific county. Many long-time gardeners in your area will also know these dates from experience.

The number of days between your last spring frost and your first fall frost. Enter both dates above and the calculator subtracts one from the other, then shows the result in both days and weeks.

Enter your first fall frost date above and the calculator compares it against today's date automatically, showing how many days remain if that date is still ahead, or how many days have passed if it is behind.

No. Published frost dates are statistical medians, typically the point at which frost has a roughly 50% chance of still occurring in the historical record for that station. Roughly half of all years see frost after the average last frost date. Treat it as a planning average, not a promise, and hold your most frost-tender transplants back a week or two past it if you want a wider safety margin.

It depends on the crop. University of Minnesota Extension groups common vegetables into four timing cohorts: roughly 8 weeks before last frost for slow starters like celery and leeks, 6 to 8 weeks for classic transplants like tomatoes and peppers, 4 to 6 weeks for cool-tolerant crops like broccoli and lettuce, and 2 to 3 weeks for fast vining crops like cucumbers and squash. Enter your last frost date above to see the actual calendar dates for each group.

Tomatoes are frost-tender, so they are normally moved outdoors on or shortly after your last frost date, not before it. Indoors, University of Minnesota Extension puts tomato seed-starting at 6 to 8 weeks before that same date, which is timed to produce a transplant that is ready to go in the ground right around when the frost risk clears.

A plant hardiness zone, published by USDA, describes typical winter minimum temperatures and is mainly used to decide whether a perennial plant can survive winter in your location. A frost date describes a specific point in the growing calendar. Zones do not tell you when to plant in spring; frost dates do, which is why this calculator works from frost dates rather than a zone number.

It may be close but is not guaranteed to match exactly, since different publishers can draw from different station records or averaging periods. This calculator does not publish its own database of frost dates at all; it runs the season-length and planting-window math on whatever dates you enter, so the result is only as accurate as the dates you provide, from any source you trust.

Frost-tender crops such as tomatoes, peppers, cucumbers and squash can be damaged or killed by a frost that occurs before your area's typical last frost date, since the date describes a rough halfway point in the historical risk, not a hard cutoff. Cold-tolerant crops such as broccoli, cabbage and lettuce tolerate a light frost and are commonly planted somewhat earlier, which is reflected in the shorter weeks-before-frost window this calculator gives them.

It varies enormously by region, from under 90 frost-free days in parts of the northern Rockies and interior Alaska to nearly year-round frost-free conditions across southern Florida and parts of southern California and Texas. There is no single national average worth quoting; enter your own two frost dates above for a figure that means something for your actual location.

Yes. The math is just the number of days between two dates you provide, so it works anywhere. The seed-starting windows in the reference table follow University of Minnesota Extension's guidance, developed for a US growing climate, so treat those specific week counts as a reasonable starting point rather than a locally calibrated figure if you are gardening outside the US.