A new method is proposed for the estimation of monthly degree-day values from monthly mean temperatures. This can be used to calculate figures for sites which are distant from the 17 sites in the UK for which published data are available, and to modify published figures to non-standard base temperatures. The new method is simpler than existing procedures and is shown to be more accurate at five sites in the United Kingdom. It is shown to be compatible with existing methods and therefore also usable outside the United Kingdom.