Tax due on property income more than expected?

[dragontree]

Hi, I'm employed and rent out a property. Declared my profit of 2,800 on return and tax due is £ 850. Thought this rather high and is way more than 20% of profit I thought Id be due, around £560. I actually tried completing return, omitting rent profit and tax came up as due £250! How could I be due more tax purely for my employment when I paid by paye thro year? HMRC had my salary and tax amounts pre filled. I'm baffled by this, hoping someone has some info on how this can be?

[someone]

Do you have any P11D benefits? Health insurance could well account for 250 in tax due if it's not already covered by your tax code.

Did you make more in pension contributions in previous years?

Did you make gift-aidable charitable donations in previous years?

The tax code HMRC assign you is their best guess at collecting the right tax. Sometimes they get it surprisingly accurate but other times they get it so far out it's a joke. If something has changed from the previous year and HMRC don't know yet then your tax code will be wrong.

(As one example - very large pension contribution made in one year using up all of the carry-forward available - all documented in the white space of the tax return - HMRC then provided a tax code that assumed that the same pension contribution would be made (and deductible) in the next year even though they knew that the maximum that could be made was 40K - underpaid tax would have exceeded 20K!)

[dragontree]

Thanks for help. I looked at my tax code and think I worked it out. Its to do with me having married allowance code from my employment but tax calculated with £12500 allowance on tax return. Im unsure if I was entitled to married allowance for 19/20, need to check wife's return, see what she earned. If she more than allowed I guess that extra tax is due.
Thanks again for help