interest on mortgage

If I've understood correctly I can claim 20% of the interest I've paid on my mortgage for my rental property. However, where on the form should I put this figure. When I put it in 'residential property finance costs' it doesn't show up in later calculations on the summary page. Thanks

Hi,
You enter the mortgage interest in the box for residential property finance costs.  
Self assessment will then add a line to the calculation after your liability is calculated, giving a deduction of 20% of the morgage interest is terms of tax.
Thank you.

Not HMRC...you dont claim 20%, you claim the full amount of the mortgage interest paid (if all borrowing related to the purchase) and the calculation then gives you relief at 20%. If this figure doesnt appear its because you dont have assessable property profit in the year, it doesnt matter if you have other assessable income, you must have assessable property profit to offset the tax credit...in which case you should carry it forward.