> For the complete documentation index, see [llms.txt](https://climashield.gitbook.io/climashield/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://climashield.gitbook.io/climashield/weather-derivatives/heating-degree-days-hdds.md).

# Heating Degree Days (HDDs)

HDDs Season= 15 May to 15 Sept

HDD = max (Tref - Tn , 0)

where,

Tref = A reference temperature below which heating is considered to be required.

Tn  = Average Temperature of the nth Day.