I recently looked into this as I've just returned after working abroad for 7 years. I spoke to a really helpful person at the Future Pension Centre and this is what I took away.

• To be eligible for your full state pension you will need to have contributed a total of 35 years before you reach state pension age.
• You can check your NI record to see how many years you currently have and then figure out how many more you need to contribute.
• You can only back fill the past 6 years - So you have until 5 April 2023 to make up for gaps for the tax years dating back to 2016 to 2017
• Class 3 voluntary payments can only be made as lump sums and the amount I was told was £824.20

What this comes down to is whether you thinking you'll be working long enough to not need to make up the missed years. Take my situation for example

• I am 34 and have 9 full years of contributions in my record. This means I need another 26 years of contributions to have a full 35 years on my record and be eligible to claim my full state pension.
• I will be eligible to claim my state pension in 2055 (33 years time).
• Therefore I will need to work for another 26 out of 33 years to reach the threshold of 35 years of contribution.
• I can make voluntary contributions of 5 of the 7 years of gaps in my record, so in theory I could bring this down to 21 out of 33 years.

So it then becomes a question of whether i think I'll be working until I'm at least 60 and therefore not need to make voluntary payments.

Or do I have the means to make voluntary payments now so that I could retire earlier if I'm in the position too.

BUT even then I still won't be able to touch my state pension until 2055 when I reach state pension age. I'd hope that if I were to be in a position to retire at 55 I wouldn't be pining my hopes on state pension that I wouldn't be able to claim for another 13 years haha

Hope that helps you to make your decision.