For example, if you retire at age 58 years and 3 months, your reverse commutation factor is worked out as follows:
We first calculate two factors, each linked to a different part of your benefits, depending on when they were built up.

Pre 1 April 2022 benefits 
Post 1 April 2022 benefits 
Factor at 58

33.23 
30.1

Factor at 59

32.16

29.22

 Pre 1 April 2022 factor at 58 years 3 months = factor at 58 + [(factor at 59 − factor at 58) x 3/12] = factor to be used
 33.23 + [(32.16 – 33.23) x 3/12] = 33.23 + (0.2675) =32.9625
 Post 1 April 2022 factor at 58 years 3 months = factor at 58 + [(factor at 59 – factor at 58) x 3/12] = factor to be used
 30.1 + [(29.22 – 30.1) x 3/12] = 30.1 + (0.22) =29.88
We then combine these factors together based on how much of your benefits were built up before 1 April 2022 and how much were built up after that date.
For example, if you have £10,000 per annum of Retirement Income Builder pension built up in total, with £7,500 built up before 1 April 2022, and £2,500 after 1 April 2022, then in percentage terms 75% (£7,500/£10,000) of your benefits relates to pre 1 April 2022 benefits, and 25% relates to post 1 April 2022
The overall reverse commutation factor is therefore calculated by combining the two factors in this proportion, as follows:
Overall factor = (pre 1 April 2022 percentage x pre 1 April 2022 factor) + (post 1 April 2022 percentage x post 1 April 2022 factor)
= 75% x 32.9625 + 25% x 29.88 = 24.7219 + 7.47 = 32.1919
This means that for every £1,000 of lump sum you exchange, you will receive £31.06 (1,000/32.1919) of gross annual Retirement Income Builder pension in return.