I submitted a late return for a client, 16/17 and submitted/paid 31/01/19. Let's say tax was £10,000, save for a day here and there rounding I make that:
01/02/18 - 20/08/18 202 days at 3.00% so £166.
21/08/18 - 31/01/19 163 days at 3.25% so £145.
Total interest £311.
HMRC have now processed and updated their screens, they get £311 (yay!) but we told the client £274, as we fed the figures into the HMRC 'estimate your penalty' pages and that was what it told us (and we took it at its word). Just re-fed the figures in and got the £274.. it's not even close, the dates would have to change by over a month to get that... am I being daft? If someone has 30 seconds could they try it (and/or explain to me why it is different) as, while it doesn't matter (other than me having to explain to the client we trusted HMRC when we should have done the calc ourselves) it is perturbing me...
And posted annonnnymouseleee out of shame, so I will thank you in advance for solving this riddle for me!