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Daily Modified Growing Degree Days

Measure daily crop heat accumulation using base and upper thresholds, with distinct Celsius and Fahrenheit modes.

  • Formula & worked example
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

A daily high of 25 °C and low of 15 °C above a 10 °C base give 10 Celsius degree-days.

Daily GDD = [min(cap,max(base,high)) + max(base,low)]/2 − base.

Worked example

Enter these known values and leave the other values blank.

Which temperature unit will you be using?
Celsius
Daily maximum temperature
25 °C
Daily minimum temperature
15 °C
Growing degree units (GDU)
10 °C -days

Assumptions and limitations

  • Daily temperature differences are degree-days, not absolute temperature readings. Celsius and Fahrenheit mode values differ by a factor of 1.8; add days only within the same scale.
  • The default corn thresholds are 10 °C/30 °C or 50 °F/86 °F. Both daily temperatures are floored at the base and the daily maximum is capped at the upper threshold. A whole day below base contributes zero.
  • The retained domain requires daily maximum strictly greater than minimum. Threshold cap must exceed base. Crop, cultivar and development stage determine valid thresholds; one day does not predict a harvest date.
  • The minimum is floored, not upper-capped, in this published modified-GDD convention. Very warm minimum temperatures are handled by that stated formula; choose a crop-specific method where this convention is unsuitable.

Common questions

What does the result describe?

Daily temperature differences are degree-days, not absolute temperature readings. Celsius and Fahrenheit mode values differ by a factor of 1.8; add days only within the same scale.

References

Floor the daily maximum at the crop base before applying its upper cap, so a whole day below base contributes zero degree-days instead of a negative total. Enforce the documented finite physical, count and denominator domains.

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