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What does Section 24 actually cost you?

Since 2017, mortgage interest on a UK buy-to-let isn't fully deductible — HMRC restricts it to a 20% basic-rate credit. Most landlord software shows your accounting net and stops there. Enter a few rough numbers and we'll show you the gap between that and what HMRC actually sees.

Annual interest only — not capital repayments

Insurance, repairs, agent fees — exclude mortgage interest

Salary, self-employment, pension etc.

Nothing is stored. Numbers are POSTed once and discarded. Output is an estimate; your accountant reconciles to your return. The arithmetic is the same one HMRC uses.