Capital or revenue?
Built around HMRC's own Property Rental Toolkit, this tool tackles the errors that trigger enquiries. The biggest is treating a capital improvement as a repair (a new extension is capital, fixing the roof is revenue) and claiming it in full against your rent.
Replacement relief and what's allowable
A capital-vs-revenue classifier tells you which is which, a replacement-of-domestic-items calculator works out the like-for-like amount you can actually claim (the old 10% wear-and-tear allowance is long gone), and a reference list separates what's allowable from what isn't.
The errors HMRC looks for
It also lists the common errors HMRC looks for, from claiming the full mortgage interest instead of the Section 24 credit (20% up to 2026/27, 22% from 2027/28) to initial repairs on a run-down purchase, so you can sense-check your return before you file.