If you have ever worked part-time, the pension is first assessed as if you had worked whole-time throughout your service. Then account is taken of the part-time service you have accrued as a proportion of whole-time service.
if you retire at age 55 having worked whole-time for 20 years and half-time for 6 years (i.e. 26 calendar years) the starting point for working out your pension would be to assume you had worked whole-time throughout those 26 years. Even if you have been working half-time during your final year, average pensionable pay is based on the whole-time pay. Let's suppose it is £36,000.00. The whole-time pension would be –
(20 x 1/60) + (6 x 2/60) x £36,000 = 32/60 x £36,000 = £19,200.00 a year
Then account is taken of the hours actually worked during the calendar length of service:
20 + (1/2 x 6) = 23 years
The whole-time pension is then multiplied by the actual length of service as a proportion of the whole-time length to give the "part-time" pension –
23/26 x £19,200.00 = £16,984.62 a year.