Flat Rate VAT calculation possibly wrong?

[brettadduco]

Hi, I’m having a problem with the Flat Rate VAT calculations.
Using cash accounting with a flat rate of 13.5%

I have not input all accounts yet, but just 1 invoice, so calculations should be easy.

Customer invoice
Services £1,511.25
VAT @20% £302.25
Total £1813.50

So by my calculations, and this is possibly where things are awry:-
we should pay HMRC
1,511.25 * 0.135 = 204.02

However, when I run a VAT return its shows that I should pay HMRC £244.82

Which is 13.5% of the total invoice amount ie (Services + VAT) * 13.5% where I was expecting to be paying (Services) * 13.5%

Have I just used the wrong calculation?

Thanks
Brett

[Lurch]

Flat rate is calculated on gross turnover, so 13.5% of £1813.50.

https://www.gov.uk/vat-flat-rate-scheme/how-much-you-pay