Once you have a private pension, you are eligible for 20% tax relief
To accumulate £100 in your pension pot, you pay in £80 and the government will pay £20 in tax relief
SIPPs share the significant tax benefits common to other private pensions; of course, HM Revenue & Customs can make changes but at present, here’s what you can expect as a UK tax payer:
If you are paying the basic rate and have £10,000 to invest in your SIPP, the government tax relief of 20% means it will rise by £2,500, so you end up with £12,500 in your SIPP.
If you are a taxpayer on a 40% tax-rate and have £10,000 to invest, the government will still provide 20% tax-relief, adding £2,500.
Then, you can claim back an additional 20% via your Self-Assessment tax return, which would take the total tax relief up to £5,000, so you will have personally contributed £10,000 to have £15,000 in your SIPP.