If you have an incomplete contribution record for a particular tax year, you will receive a statement advising you of the position, usually about 20 months after the end of the year in question. The statement will also show the amount of voluntary contributions required to complete the contributions record for that year. This could be worthwhile if it is unlikely that future contributions from earnings will give you a full state pension, e.g. if you’re close to retirement age. If you're unsure whether an incomplete record exists for a previous year,  you can check your contributions record via your personal tax account. HMRC has extended the deadline for making up any contributions shortfall as voluntary contributions can now be paid (at 2022/23 rates) by 5 April 2025 in respect of any years from 2006/07 to 2017/18.

The new service allows you to check whether paying Class 3 contributions is likely to increase your state pension entitlement, make a payment with an immediate confirmation, and is digital from end to end, i.e. you no longer need to contact HMRC for a reference number.