Growing Degree Days Calculator
Adds up heat over a period, to compare with what a crop or pest needs to develop.
Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
The formula
simple: GDD = max(0, (high + low) ÷ 2 − base) capped: GDD = (min(high, upper) + max(low, base)) ÷ 2 − base
Both are base temperature methods. The capped version holds a hot day at the upper limit and a cold night at the base, because crops stop gaining beyond those points. For a day below base, the high is held at the base as well.
What to watch out for
A typical high and low over many days only approximates a day-by-day count, because it hides days that fall below the base, so use the log for a season’s figure. Other crops use other bases: check your crop guide.
Frequently Asked Questions
How do you calculate growing degree days?
Take the day’s high and low, average them, and subtract the base. A 26 °C high and 14 °C low on a 10 °C base gives 10 degree days.
What is the 86/50 method?
The US maize method, in °F. Highs above 86 count as 86 and lows below 50 count as 50. A 95 °F high and 45 °F low gives 18 degree days, where a simple average would give 20.