What base temperature should I use?

Base temperature varies by crop and pest. Common values: corn and soybeans use 50°F (10°C), wheat uses 32°F (0°C), many insects use 50°F (10°C). Check university extension resources for your specific crop or pest.

What is the upper cap temperature for?

Some crops stop responding to heat above a ceiling temperature (often 86°F / 30°C for corn). Setting an upper cap replaces values above the cap with the cap value before calculating, preventing overestimation on extremely hot days.

What happens when the low temperature is below the base?

Daily GDD cannot be negative. If the average of high and low is below the base temperature, that day contributes 0 GDD — it is simply a cold day with no accumulated heat units.

How is daily GDD calculated?

The standard single-sine or simple average method: GDD = ((High + Low) / 2) − Base. Temperatures are first capped at the upper threshold if one is set, and the result is floored at 0.

Can I switch between Fahrenheit and Celsius?

Yes. Use the unit toggle at the top of the tool. All inputs and the base/cap temperatures will switch units, and the GDD total is recalculated automatically.

Why do GDD totals differ between sources?

There are several GDD calculation methods (simple average, single sine, double sine). This tool uses the widely accepted simple average method. More sophisticated methods use hourly temperature curves but require more data.

Growing Degree Day Calculator

Enter daily high/low temperatures and a base temperature to calculate Growing Degree Days for crop and pest development forecasting.

Temperature Settings

Base Temp (°F)

e.g. 50°F for corn

Upper Cap (°F, optional)

e.g. 86°F for corn

Daily Temperature Data

High (°F)

Low (°F)

Enter temperature data and click Calculate GDD to see results.

Total GDD

heat units

Days

entered

Avg GDD/Day

heat units

Common Crop Benchmarks

Daily Breakdown

Day	High	Low	Avg	GDD	Cumulative

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Summary

Growing Degree Days (GDD) measure accumulated heat above a base temperature threshold, giving farmers and gardeners a reliable way to track biological development independent of calendar dates. Each crop or pest has a known GDD requirement to reach key growth stages. By summing daily GDD values from planting date onward, you can predict when a crop will flower, reach maturity, or when a pest will emerge — even if the actual calendar dates shift year to year due to weather variation.

How it works

Enter the daily maximum (high) temperature.
Enter the daily minimum (low) temperature.
Set the base temperature for your crop or pest (default 50°F / 10°C).
Optionally set an upper cap temperature to prevent over-counting on very hot days.
For a date range, click "Add Day" to input consecutive days of temperature data.
The tool sums GDD values and displays a running total.

Use cases

Predict corn, soybean, or wheat maturity dates based on accumulated heat units.
Track pest emergence windows such as corn rootworm or codling moth.
Plan irrigation and fertilizer timing aligned with crop growth stages.
Compare growing seasons across years using consistent heat-unit benchmarks.
Estimate apple or grape harvest windows for orchard and vineyard management.
Monitor turf growth for lawn care scheduling.
Track vegetable crop development from transplant to harvest.
Calculate heat accumulation for forestry pest management programs.

Frequently Asked Questions

Last updated: 2026-06-13 · Reviewed by Nham Vu