How to use the growing degree days calculator
- Choose Fahrenheit or Celsius.
- Type the high and low temperature for each day, one day per line, high first.
- Enter the base temperature. The 50 F and 10 C shown are examples, so use the base for your own plant or insect.
- Open More options for the cutoffs method or to enter a goal, then read the total and the running total by day.
Formula
simple average: degree days = (high + low) / 2 - base, never below 0
with cutoffs: each temperature is first limited to the range from the base to the upper cutoff
running total = the sum of the daily degree days so far
Growing degree days measure accumulated warmth above a base temperature. They do not measure moisture, light or soil.
Five days with a base of 50 F
Highs and lows of 72/50, 80/58, 88/64, 55/41 and 68/49 give daily averages of 61, 69, 76, 48 and 58.5. Above 50, that is 11, 19, 26, 0 and 8.5 degree days, which total 64.5. The running total after each day is 11, 30, 56, 56 and 64.5.
With cutoffs at 50 and 86, the 88 high counts as 86, and the 41 low counts as 50, so the days score 11, 19, 25, 2.5 and 9, which total 66.5. In Celsius with a base of 10 and a cutoff of 30, highs and lows of 22/10, 25/12, 31/14 and 8/2 total 26.5.
Choosing the method
The simple average treats a cold day as zero and ignores the shape of the day. The cutoffs method limits both temperatures to the range where growth takes place, so very cold nights count as the base and very hot afternoons count as the upper limit. Neither is exact, and they give different totals, so use the same method as the source of your target numbers.
A base temperature is not universal. Different crops and insects have their own bases and goals, so take them from a reliable source for your own crop or pest. This page does not supply them.
Related garden tools
Plan sowing dates with the Planting Schedule Calculator, set rows apart with the Plant Spacing Calculator, and size beds with the Raised Bed Soil Calculator. For larger plantings, see the Trees per Acre Calculator, and for a spread of temperatures, the Descriptive Statistics Calculator.
Assumptions and limits
- Each day is described by one high and one low temperature.
- The base and the upper cutoff are values you choose, with examples shown.
- The simple average never counts a day as negative.
- Only the first 60 days appear in the table, but all days are counted in the total.
Frequently asked questions
How do I calculate growing degree days?
Average the daily high and low, subtract the base temperature, and use zero if the result is negative. Add the daily values to get the total. Five sample days with a base of 50 F total 64.5.
What base temperature should I use?
Use the base for your plant or insect from a trustworthy source. The 50 F or 10 C shown is only an example.
What does the cutoffs method do?
It limits each temperature to the range between the base and the upper cutoff before averaging. That stops very cold nights and very hot afternoons from distorting the daily value.
Can I track progress toward a stage?
Enter a goal in More options. The page shows the degree days still to go and how many days that takes at the average pace so far.