If you inherited a flat and chose to let it, moved in with a partner and let your old place because the market would not bear a quick sale, or moved abroad for two years and let your home while you were away, you are what HMRC calls an accidental landlord. From the day you took the first month's rent, the same compliance machine that applies to a portfolio investor with twenty doors applies to you. This guide is the one-page journey map: every tax touchpoint you will hit, in the order you will hit them, with one forward-link per topic to a deeper page. We cover the six-month HMRC notification reflex under TMA 1970 s.7, what counts as taxable rental income (gross-of-mortgage-interest), what you can actually deduct (including the post-2016 replacement of domestic items relief under ITTOIA 2005 s.311A), the Section 24 mortgage-interest reducer at 20 percent, the Making Tax Digital for ITSA threshold cascade (£50,000 from April 2026, £30,000 from April 2027, £20,000 from April 2028), capital gains tax on eventual sale (residential 18 / 24 percent, final 9 months deemed-residence under TCGA 1992 s.223(1), lettings relief narrowed to shared-occupation lodger-style cases only under s.223B since FA 2020), the 60-day in-year CGT return clock starting at completion of sale not exchange, and the Let Property Campaign catch-up route if you have already been letting for some time without telling HMRC. Closing checklist covers the five most-missed points (notification even at sub-personal-allowance profit, consent-to-let, probate base cost, PPR election with two homes, 60-day clock from completion).