Richard

Thanks but, as noted, my tax code notice says I owe just over £400 and that my tax-free allowance has been reduced by just over £3,500. The amount owed is 12% of the tax-free allowance adjustment (reduction). Given that there is no 12% tax rate, how could this be - why isn't the restriction five times the amount owed (i.e. calculated at a 20% tax rate)? Any ideas?

Based on my self-assessment for 2022-23, I owe HMRC around £400. On my tax code for 2023-24, there is an adjustment (reduction) of around £3,500 in my tax-free amount - i.e. more than eight times what I owe. What's the relationship between the reduction amount and the tax owed amount? And why doesn't it seem to relate to tax rates of 20% or 40%?