Heating Degree Day Calculator
Heating Degree Day Calculator works out Degree units for the day and Accumulated over the period from Mean temperature for the day, Daily maximum and Daily minimum. The default figures on this page give degree units for the day of 8; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
2 steps
- Mean temperature used: 10
- Heating degree units = max(base - mean, 0) = max(18 - 10, 0) = 8
Its 5 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
2 sources
What the Heating Degree Day Calculator calculates
Accumulates growing, heating or cooling degree days from daily temperatures against a base temperature.
How to use this Heating Degree Day Calculator
Enter Mean temperature for the day, Daily maximum, Daily minimum and Base temperature. Degree units for the day updates as you type. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Degree units for the day, Accumulated over the period and Mean temperature used.
The method follows Growing degree days accumulate max(mean - base, 0); heating degree days accumulate max(base - mean, 0); cooling degree days accumulate max(mean - base, 0). and NOAA National Weather Service, degree day definitions.
What you can compare
Change one input at a time to see how it affects Degree units for the day, Accumulated over the period and Mean temperature used. The inputs you can vary are Mean temperature for the day, Daily maximum, Daily minimum, Base temperature, Upper cutoff and Number of days like this.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
How do you calculate Heating Degree Days?
Accumulates growing, heating or cooling degree days from daily temperatures against a base temperature. Open “How this is worked out” beside the result to see each step for your own figures.
What does Heating Degree Days mean on an electric bill?
Accumulates growing, heating or cooling degree days from daily temperatures against a base temperature. On this page it is computed from Mean temperature for the day, Daily maximum and Daily minimum and shown as Degree units for the day, Accumulated over the period and Mean temperature used.
What is meant by Heating Degree Days?
It needs Mean temperature for the day, Daily maximum, Daily minimum, Base temperature, Upper cutoff and Number of days like this. Nothing else is required, and the figures stay in your browser.
How do you count degree days?
The result gives Degree units for the day, Accumulated over the period, Mean temperature used and Type, each labelled with its unit so the figure can be read on its own.
What information do I need for the Heating Degree Day Calculator?
You need Mean temperature for the day, Daily maximum, Daily minimum, Base temperature, Upper cutoff and Number of days like this. The page opens with default figures that give degree units for the day of 8, so you can see the scale before entering your own.
What does this Heating Degree Day Calculator show?
It shows Degree units for the day, Accumulated over the period, Mean temperature used and Type, with the working and any warnings for your entries.