AP can be purchased either by a lump sum or by regular monthly contributions over a pre-specified term. The costs are shown per £250 pa of AP purchased.

Generally, factors for calculating the cost to a member of AP should be selected with reference to the member's:

• age (last birthday) at election
• expected normal pension age (NPA) at retirement (NPA is defined as a member's state pension age (or 65, if that is higher) in the career average
  section). For the purpose of this guidance, a member's expected NPA in the career average section is as defined in HMT Directions,
• chosen form of payment (either lump sum or regular contribution), and
• chosen form of benefit (either member only or member with dependant).

Where the AP is not purchased by a lump sum, factors must additionally be chosen with reference to:

• the date of election, and
• the period of contributions as at the election date (between 1 year and 20 years).

Where the member has a non-integer NPA a contribution rate is calculated for the member's NPA rounded down to the nearest whole number. A further contribution rate is calculated for the member's NPA rounded up to the nearest whole number. These figures are interpolated to obtain the actual contribution rate.

Where the member elected to purchase the regular contribution AP contract after 22 June 2010, the AP will increase in line with Consumer Prices Index (CPI) before coming into payment.

Where the member elected to purchase the regular contribution AP contract on or before 22 June 2010, the AP will increase in line with Retail Prices Index (RPI) before coming into payment.

Factors for new lump sum elections are contained in Tables x-702 to x-705.

Factors for regular contribution elections made after 22 June 2010 are contained in Tables x-706 to x-715.

Factors for regular contribution elections made on or before 22 June 2010 are contained in Tables x-716 to x-719.

Factors for the purchase of the outstanding amount by lump sum (for elections made on or before 22 June 2010) are contained in Tables x-720 to x-721. Factors for the purchase of the outstanding amount by lump sum (for elections made after 22 June 2010) are contained in Tables x-701 to x-705.