Start with a WAG if you don't have an FMS:
Normal TOD is about 100 NM; normal time of flight after TOD is about 30 minutes, for about 5 NM/minute on average.
60 Kt = 1 NM/minute, or 30 NM over the course of the descent, so a good wind correction is half the wind. Assume average wind is half the wind at cruise. Therefore:
TOD correction = 1/4 head/tail wind component at cruise.