Calculator
Fill the fields, then press Calculate. Results appear above this form.
Formula used
This tool estimates a harvest window using one of two maturity methods, then applies your adjustments.
- DTM method: maturity_days_est = DTM
- GDD method: avg_gdd_day = max(0, avg_temp − base_temp), then maturity_days_est = ceil(required_gdd / avg_gdd_day)
- start_date = base_date + (effective_maturity_days − early_pick_days)
- end_date = base_date + (effective_maturity_days + late_pick_days + window_days)
How to use this calculator
- Choose a crop name and select your calculation method.
- Pick the date basis that matches your seed packet guidance.
- Enter sow or transplant dates, then set maturity inputs.
- Use climate and stress factors to reflect your season.
- Set early/late allowances and harvest window length.
- Add successions if you want staggered harvests.
- Press Calculate, then download CSV or PDF exports.
Example data table
Sample values to test the calculator quickly.
| Crop | Sow date | Method | DTM / Required GDD | Climate | Window (days) | Interval (days) | Successions |
|---|---|---|---|---|---|---|---|
| Lettuce | 2026-02-05 | DTM | 55 | Cooler (+10%) | 14 | 3 | 2 every 14 days |
| Tomato | 2026-03-01 | DTM | 70 | Normal (0%) | 21 | 4 | 1 |
| Sweet corn | 2026-03-15 | GDD | 650 | Warmer (-7%) | 10 | 2 | 3 every 10 days |
Harvest window planning guide
1) Why harvest windows matter
Harvest timing is not a single date. Most crops deliver quality over a window that depends on variety, weather, and how fast you can pick. For example, lettuce can be harvested for 7–14 days, tomatoes often for 21–35 days, and sweet corn is usually best within 3–7 days after reaching peak maturity.
As a rule, the shorter the peak quality period, the more important your picking frequency becomes. Sweet corn can lose sweetness within a day in warm weather, while curing onions and winter squash can store for months when dried properly.
2) Using maturity targets with real dates
Seed packets commonly list “days to maturity” from sowing or transplanting. This calculator converts your chosen basis into an estimated first-harvest date, then expands it into an early and late edge using your allowances. If you track actual first harvests, update the maturity target to tighten future estimates.
3) Temperature, heat, and frost effects
Temperature shifts maturity speed. A warmer season can shorten time-to-harvest, while cool periods can extend it. Frost risk is crop-specific: many warm-season crops are damaged near 0 °C, while hardy greens can tolerate light freezes (around −2 °C) when acclimated. Use the climate and stress factors to reflect these realities.
4) Spreading harvest with successions
Succession planting reduces “all-at-once” harvests. If your harvest window is 10 days and you sow every 10–14 days, you can keep steady picking without overwhelming storage or labor. Fast crops like radish and salad greens suit short intervals; slower fruiting crops benefit from fewer, larger successions.
5) Recordkeeping that improves accuracy
Log three items: planting date, first harvest date, and when quality drops. After one season, compare your notes to the calculator’s window. If you consistently harvest earlier or later, adjust the maturity target or allowances. This turns the calculator from an estimate into a calibrated schedule for your site.
FAQs
1) What does “harvest window” mean?
It is the range of dates when a crop is typically harvestable at good quality, from the earliest likely harvest through the latest practical harvest, based on your inputs and allowances.
2) Should I use Days to Maturity (DTM) or Growing Degree Days (GDD)?
Use DTM when you only have packet days or you are starting. Use GDD when you track temperatures and have a known GDD target, because it often predicts timing better across variable seasons.
3) How does the climate adjustment change results?
The climate adjustment applies a percentage change to the maturity time. Warmer settings reduce estimated days; cooler settings increase them. It is a controlled way to reflect seasonal acceleration or delay.
4) What early/late allowance should I choose?
Start with 3–7 days for quick greens and 7–14 days for many fruiting crops. Increase the allowance if you expect uneven irrigation, variable sunlight, or wide temperature swings.
5) Can I plan staggered planting dates?
Yes. Enable successions, set the number of plantings, and choose an interval (days). The calculator offsets each start date and generates a separate harvest window for every succession.
6) What base temperature should I use for GDD?
If you do not know it, 10 °C (50 °F) is a common default for many warm-season crops. Cool-season crops can use lower bases. Use the value from your local extension guidance when available.
7) How accurate are the outputs?
They are planning estimates. Accuracy improves when you use consistent date basis, realistic stress factors, and your own garden records. Treat the window as a schedule range, not a guarantee.