GDD to Maturity & Count Down to Harvest on Heat Units
Tracks maize
Crops develop on heat, not the calendar — enter the growing degree days your crop needs, the GDD it has already gained and the GDD it adds per day to get the remaining heat units, days to maturity and progress to harvest.
Estimate days to maturity
Next: at the current pace of 15 GDD/day the crop should reach maturity in about 40 days; warm spells shorten this and cool spells stretch it, so re-check after a weather swing.
Growing Degree Days sum the daily heat above a crop base temperature; maturity tracks accumulated heat far better than a fixed calendar count of days.
GDD to maturity — key facts
- Remaining GDD
- required − accumulated
- Days to maturity
- remaining GDD ÷ daily GDD
- Progress
- accumulated ÷ required (≤ 100%)
- Daily GDD
- (avg temp − base temp)
- Maize to maturity
- ≈ 1300–1700 GDD by hybrid
- Typical daily GDD
- ≈ 15–25 in mid-season
- Why heat units
- weather-proof crop staging
- Privacy
- Runs in your browser; nothing uploaded
Crops keep time in heat, not days
A maize hybrid does not mature on a fixed calendar date — it matures when it has banked enough warmth. Growing degree days measure that warmth: each day above the crop's base temperature adds heat units, and the crop reaches a stage once the running total hits the threshold for that stage. A warm spell speeds the countdown; a cool one stretches it. Counting down the remaining heat units is therefore a far better guide to harvest than ticking off days on a calendar.
This tool turns required GDD, accumulated GDD and daily GDD into the remaining heat units, the days to maturity and progress to harvest. Use it to schedule harvest, drying and the following crop, to compare fields and seasons on the same scale, and to spot a late crop early. Pair it with the Field Establishment, Plant Population Yield Response and Seed Replacement Rate tools to plan the crop from stand to harvest.
Schedule harvest
Know the days left before the crop is ready.
Beat the weather
Heat units stay accurate across warm and cold years.
Spot a late crop
See if progress is behind for the time of season.
Works any crop
Maize, wheat, soybean, sorghum and more.
Frequently Asked Questions
How does the GDD to maturity calculation work?+
The remaining heat units are the GDD required minus the GDD already accumulated, never below zero. The days to maturity is that remainder divided by the GDD your crop gains per day, rounded up. Progress to harvest is accumulated ÷ required, capped at 100%. So the tool turns three heat figures into a realistic countdown to maturity.
What are growing degree days (GDD)?+
Growing degree days are a measure of accumulated warmth above a crop's base temperature. Each day adds (average daily temperature − base temperature) degree-days, and crops develop once enough have piled up. GDD predict crop stages far better than the calendar because a warm spell speeds development and a cold one slows it.
Why use heat units instead of days on the calendar?+
A crop sown the same date in a warm year and a cold year matures on different dates, because development tracks temperature, not the date. GDD account for that: the same heat total brings the crop to the same stage whatever the weather. That is why this tool counts down remaining heat units rather than fixed days.
Where do I get the GDD my crop needs?+
Required GDD to maturity are published per crop and variety by seed companies, extension services and agricultural universities — for example a maize hybrid rated around 1300–1700 GDD to black layer. Use the figure for your variety and base temperature. The accumulated GDD comes from your local weather record since planting.
What GDD per day should I enter?+
Use a typical daily GDD for your location and season — often around 15–25 GDD a day in the main growing months for warm-season crops, less early and late in the season. The tool uses it to convert remaining heat units into days, so a realistic seasonal average gives the best estimate. Lower it for the cooling weeks near harvest.
How is progress to harvest read?+
Progress is the share of the required GDD your crop has already accumulated. At 50% the crop is roughly halfway through its heat-driven development; near 100% it is approaching maturity. It is a quick way to see how far along the season is and to compare fields or seasons on the same scale.
Does this work for any crop?+
Yes — maize, wheat, soybean, sorghum, cotton and many vegetables all develop on accumulated heat above a base temperature. Only the required GDD and base temperature change by crop and variety. Enter the values for your crop and the countdown holds.
Are the days-to-maturity figures exact?+
They are solid planning figures from your inputs. Actual maturity shifts with the weather still to come — a heatwave shortens it, a cool spell lengthens it. Treat the result as a working estimate, update the accumulated GDD as the season runs, and use it to plan harvest, drying and the next crop.