Graeme Booth

Can someone please explain the breakdown for how to calculate my income tax contribution for each band. I am a high earner based in Scotland and understand that I lose the personal allowance. What I don't understand is how that is taken account into each of the bands. So, assuming I'm on 125140 then I lose the personal allowance of £12570 completely (23-24 rates). Ok, but what does that mean to the individual bands? It was 0% on the first 12500, then 19% on the next (£14732-12571) £2161, then 20% on the next (£25688-£14733), 21% on the next band, 42% on the next and then 47% on the highest band, then with zero personal allowance the numbers in brackets are essentially reduced by 12570, ie the % is applied to the same 'difference'. But what happens at the 42%/47% level? I'm really confused. Even more when I start factoring in pension contributions, BIK, salary sacrifice etc. Ever single calculation I've seen gives me a different answer so, for the love of God, can someone just tell me explicitly how to work this out definitively. I've been hit with an HMRC unpaid bill which I'd really like to validate. However with the random number generator that is the tax system, I just cannot work it out. Seems beyond me. Help! My understanding is below: 0% : no contribution 19% of (2161-0 = 2161) = £410.78 20% of (13119-2162 = 10956) = £2191.20 21% of (31094-13120= 17974) = £3774.54 42% of (112573-31095 = 81478) = £34220.76 47% of (125140-112574 = 12566) = £5906.49 Total = £46503.77 ???