How this calculator works
The modified growing-degree-day method clips each daily extreme between a lower developmental threshold and an upper limit before averaging. The default 10 C base and 30 C cap match the common corn model described by NOAA. Thresholds and clipping conventions differ among crops and forecasting systems; compare totals only when the same method is used.
Formula
GDU = max(0, (clipped Tmax + clipped Tmin)/2 - base). Fahrenheit degree-day differences equal Celsius degree-day differences × 1.8; do not add 32.
Worked example
For Tmin = 15 C, Tmax = 25 C, base = 10 C and cap = 30 C, daily accumulation is 10 C degree-days, equivalent to 18 F degree-days. A 5 C minimum and 35 C maximum also give 10 after clipping.
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Frequently asked questions
Is a degree-day a temperature?
It is accumulated temperature difference over time. Its Celsius and Fahrenheit values differ by a factor of 1.8 without an offset.
Can I use Fahrenheit temperatures?
Yes. Each temperature field offers Fahrenheit; the engine converts absolute temperatures before calculating differences.
Is this Canadian corn heat units?
No. Ontario crop heat units use separate day and night response equations. This tool implements the modified growing-degree-day model.