I did a quick calculation on HL site: Annual income:£72,000 SIPP contribution: £20,000 You pay: £12,000 Gov adds 20%: £4,000 Extra tax relief: £4,000 (from tax return)
From HL SIPP Info: Each time we collect your Direct Debit the Government will automatically add money too. If you’re under 75 and a UK resident, you’ll get basic-rate tax relief, which works out at £20 for every £80 you pay in. If you pay tax at a higher rate you may be able to claim back more tax relief through your tax return. Pension and tax rules change and benefits depend on your circumstances.