# Heating degree day (HDD)

By Nick Bruzzi · Published 2026-07-08 · https://heatprice.com/glossary/heating-degree-day

A measure of how cold a day is for heating purposes: how far the day's average temperature falls below 65°F. A day that averages 25°F counts as 40 heating degree days (65 − 25).

Dealers and analysts add up HDD to gauge fuel demand — a stretch of cold piles up degree days, which both raises how fast you burn oil and can strain local delivery when everyone needs a fill at once.

Source: EIA / NWS heating-degree-day definition (65°F base).

## See also

- [best time to buy](https://heatprice.com/guides/best-time-to-buy-heating-oil)
- [K-factor](https://heatprice.com/glossary/k-factor)
- [Automatic delivery](https://heatprice.com/glossary/automatic-delivery)

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