Predict harvest timing from Growing Degree Days accumulation.
Choose your crop, enter the planting date, relative maturity and expected average daily temperature. The calculator applies each crop's base temperature (corn/soybean 50°F, wheat 32°F), totals required GDD, and projects the harvest date.
A farmer planted corn on April 25 and planned an October 1 combine start. The GDD estimate showed the 110-day hybrid would not reach black-layer until October 8. The extra week let him book the custom combine on a better schedule instead of waiting idly.
✓ Expert Reviewed: This calculator and its content have been reviewed by agricultural experts. Formulas are based on standard extension service recommendations. For site-specific advice, consult your local agronomist.
Enter the required input values in the form fields above. Each field includes default values that you can adjust to match your specific situation. Click the Calculate button (or simply change any input) to see instant results. Use the Metric/Imperial toggle to switch between unit systems. Results are displayed in the results panel and can be used for farm planning and decision-making.
This calculator is designed to help farmers, agronomists, and agricultural students make quick, accurate calculations for farm management. It uses standard agricultural formulas based on extension service recommendations and scientific literature. Whether you are planning inputs, estimating yields, or managing finances, this tool provides reliable estimates to support your decisions.
Daily GDD = (Tmax + Tmin) ÷ 2 − Base temperature. Base temperatures: corn and soybean 50°F (10°C), wheat 32°F (0°C). Required GDD ≈ relative maturity × crop factor (corn ≈ 25, soybean ≈ 26, wheat ≈ 20). Days to harvest = Required GDD ÷ Daily GDD. Harvest date = planting date + days to harvest.
Corn, planted April 20, 110 RM, average 70°F: base 50°F, daily GDD = 20, required GDD ≈ 2,750. Days = 2,750 ÷ 20 = 138 days. Estimated harvest ≈ September 5.
Common mistakes: using a single year's average temperature; forgetting that GDD stops above the upper cutoff (≈86°F); applying corn factors to wheat; ignoring rainfall and stress that delay maturity. Use long-term average temperatures for planning.
Growing Degree Days (GDD) measure heat accumulation above a crop's base temperature. Each day's GDD = average temperature − base. Crops develop only when GDD accumulate; maturity is reached after a species- and variety-specific total.
Corn and soybeans use a 50°F (10°C) base; winter wheat uses 32°F (0°C) for spring green-up. Daily GDD below the base is zero, not negative.
It is a planning estimate. Actual maturity shifts with heat, moisture, pests and variety. Use long-term average temperatures and treat the date as ±7 days.
Best practice uses (Tmax + Tmin)/2. If you only have the daily average, that is an acceptable approximation. Tmax above 86°F is typically capped (86/50 rule for corn).
It lets you schedule custom combines, drying capacity, labor and storage ahead of time, and compare how early vs late planting affects harvest timing across your fields.