04/24/2026
It's Favorite Formula Friday!
This week in my life contingencies class, we are diving into Woolhouse's approximation for life annuities!
When approximately converting between annual life annuities and m-thly life annuities, the two-term Woolhouse formula is a great shortcut. The trick I use to remember it: the correction term (m−1)/2m always "penalizes" for the extra payment frequency. For the temporary version, you just scale that penalty by how much of the annuity does NOT get deferred away by mortality and discounting over the policy period (i.e., multiply by 1 − n_E_x).