🌡️ Growing Degree Days (GDD) Calculator
Enter the daily high and low and a base temperature to get the growing degree days, and multiply by the number of similar days for an accumulated total.
GDD for one day
11
Accumulated over 30 similar days
330
Growing degree days measure accumulated warmth: GDD = ((daily high + daily low) ÷ 2) − base temperature, floored at zero. The base is the temperature below which a crop doesn\'t grow (commonly 10 °C / 50 °F; 4 °C for cool-season and higher for warm-season crops). Add up daily GDD to predict flowering, pest emergence and harvest. This gives one day; multiply by similar days for a rough total. 🔒 In your browser.
How the growing degree days (gdd) calculator works
Growing degree days measure the accumulated warmth a crop or insect experiences. For one day, GDD = ((daily high + daily low) ÷ 2) − base temperature, and negative results are treated as zero. The base is the temperature below which development stops — commonly 10 °C (50 °F), lower for cool-season crops and higher for warm-season ones. Add up the daily GDD across the season, or multiply a typical day by the number of days for a rough total.
GDD predicts biological timing far better than calendar days: crops flower, insects hatch and pests reach spray-worthy stages at fairly consistent GDD totals. Some methods cap the daily high (e.g. at 30 °C for corn) so extreme heat doesn't inflate the count; this tool uses the simple average method. Base temperatures and thresholds are crop-specific — check your local extension service.
Frequently asked questions
How do you calculate growing degree days?
Average the day's high and low, then subtract the base temperature: GDD = ((high + low) ÷ 2) − base, with any negative result counted as zero. A day with a 30 °C high and 12 °C low at a 10 °C base is ((30+12)/2) − 10 = 11 GDD.
What is the base temperature?
The temperature below which a crop or organism doesn't develop. It's commonly 10 °C (50 °F) for many crops, about 4 °C for cool-season plants and higher for warm-season ones like corn. Use the value for your specific crop.
What are growing degree days used for?
To predict development stages — germination, flowering, maturity — and to time pest and disease management, since insects reach each life stage at consistent GDD totals rather than on fixed dates. It's more reliable than the calendar.
How do I accumulate GDD over a season?
Add each day's GDD from a start date (often planting or a biofix). This tool gives one day's value and can multiply by a number of similar days; for precise tracking, sum the actual daily highs and lows.
Should I cap the maximum temperature?
Some crops use an upper threshold (e.g. cap the high at 30 °C for corn) so very hot days don't overstate development. This calculator uses the simple average method; apply a cap manually by entering the capped high if your crop needs one.