Growing Degree Days Calculator
Growing degree days (GDD) quantify the heat available for plant and insect development by measuring the daily mean temperature above a species-specific base temperature. Unlike calendar days, GDD track biological time: the same crop will reach a given growth stage in fewer calendar days in a warm year than in a cool year, but will always accumulate the same total GDD. Enter daily high and low temperatures along with the crop or pest base temperature to compute the GDD for a single day, or enter multiple days of totals for a seasonal accumulation.
Growing degree days formula
Mean Temperature = (Tmax + Tmin) / 2
GDD = max(0, Mean Temperature - Tbase)
Tmax and Tmin are the daily maximum and minimum temperatures in the same units as Tbase. GDD cannot be negative: if the mean temperature is below Tbase, GDD for that day is 0 (no development). The formula is used with Fahrenheit in the US and Celsius in much of the rest of the world; the accumulated totals differ by a factor of 1.8 (9/5) between F and C-based systems.
GDD requirements for common US crops (base 50 F)
- Corn emergence: approximately 115-130 GDD.
- Corn silking: approximately 1,320-1,400 GDD.
- Corn black layer (maturity): approximately 2,450-2,700 GDD.
- Soybean R1 (first flower): approximately 700-750 GDD.
- Tomato first harvest: approximately 1,000-1,200 GDD.
Growing degree days: frequently asked questions
What are growing degree days?
Growing degree days (GDD) are a measure of accumulated heat useful for predicting plant development and pest emergence timing. GDD = max(0, ((Tmax + Tmin)/2) - Tbase) for a single day, where Tbase is the minimum temperature below which development is negligible. Accumulated GDD from planting or a spring date predicts when crops will reach specific growth stages.
What is the base temperature for common crops?
Common base temperatures: corn 50 F (10 C), soybeans 50 F, wheat 32-40 F, tomatoes 50 F, apples 43 F, cotton 60 F, potatoes 40 F. The USDA NRCS and university extension services publish GDD requirements for specific crop stages, such as the approximately 2,700 GDD (base 50 F) needed for corn silking in the US Corn Belt.
How does the NWS use GDD in forecasting?
The NWS Climate Prediction Center and local forecast offices issue spring and growing season GDD outlooks. The NOAA's National Centers for Environmental Information (NCEI) tracks cumulative GDD nationwide. GDD departures from normal indicate whether crops are ahead or behind schedule, affecting harvest timing forecasts and pest control recommendations.
What is the maximum temperature cap in GDD calculations?
Many GDD methods cap Tmax at an upper threshold (often 86 F / 30 C for corn) because above that temperature, additional heat provides no developmental benefit. The modified method uses: if Tmax > 86 F, use 86 F; if Tmin < 50 F, use 50 F; then GDD = (Tmax_adj + Tmin_adj)/2 - Tbase. This calculator uses the standard (uncapped) method.
Are growing degree days the same as heating degree days?
No. Growing degree days (GDD) measure heat accumulation above a base temperature relevant to plant or pest development. Heating degree days (HDD) and cooling degree days (CDD) measure departure from 65 F for energy demand forecasting. The calculation method is similar, but the base temperature and application are completely different.
Official sources
- NOAA NCEI: Growing Degree Day Data.
- USDA NRCS: Growing Degree Days for Agriculture.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.