CGT planning in Pinner: the accidental landlord's PRR calculation, explained properly
HA5's modal tax event is the sale of a former main residence that was let for a period. Private residence relief, the final-9-months rule, and a much-narrower lettings relief than most owners assume — the maths is specific, and it is routinely done wrong.
Why Pinner is different
Pinner's property tax pattern is dominated by a single scenario: the accidental landlord. A couple buys a home in HA5, lives in it for some years, then moves out — for work, for children's schooling, for a relationship change, sometimes just because the market was too slow to sell into. Rather than accept a discounted sale, they let the property. Three, five, seven years later the market has moved and they finally sell. What arrives in the post four months after completion is a CGT bill that their solicitor didn't flag, their general accountant estimated conservatively, and neither of them ever fully explained.
The calculation is distinctive because it is not a pure buy-to-let disposal (which would be fully taxable) and not a pure main-residence disposal (which would be fully exempt under private residence relief). It is a hybrid: PRR covers the period of occupation, the final 9 months of ownership are also exempt, and the remainder of the letting period is taxable on a time-apportioned basis. Then lettings relief might apply — but only in a very narrow set of circumstances that almost no accidental landlord actually meets.
Lettings relief is where the conversation with a generalist most often goes wrong. Before April 2020, lettings relief was available to anyone who had let out a property that had been their main residence, up to a £40,000 cap per owner. That is the version most accountants and online calculators still reflexively apply. The rules changed: since April 2020, lettings relief is only available where the owner was in shared occupation with the tenant during the letting period. For a Pinner couple who moved out completely and then let the property — which is 90%-plus of the scenario — lettings relief simply does not apply. Applying the old rule overstates the relief by £9,600 per owner (£40,000 cap × 24% higher rate), and when HMRC spots it in a compliance check, interest and penalties follow.
The second error is rarer but costlier: getting the base cost wrong. PRR time-apportions the gain, so the base cost is effectively held fixed — but the improvements during the occupation period (which would have been irrelevant when the property was fully PRR-exempt) suddenly become valuable once a portion of the gain is taxable. A 2014 loft conversion, a 2017 rear extension, a 2019 kitchen refit — these reduce the base gain and therefore the taxable gain in proportion. Pinner specifically benefits here: Harrow Council's Building Control records for HA5 are well-indexed from about 1998 onwards, which makes improvement-cost reconstruction reliable in a way it is not in some neighbouring boroughs.
Worked example: HA5 'bought it, lived in it, couldn't sell, let it, sold it' disposal
A Pinner couple, higher-rate taxpayers, jointly own a three-bedroom house in HA5. Purchased August 2016 for £525,000. Occupied as main residence 2016–2021 (5 years). Relocated to Hertfordshire mid-2021; property let out from August 2021 at £2,300/mo. Now selling in 2026 for £745,000. Ownership period 9 years 6 months (114 months). Occupation period 5 years (60 months). Letting period 4 years 6 months (54 months). No shared occupation during letting. During ownership, one documented improvement: a £28,000 loft conversion completed in 2019, with Building Control sign-off and invoices retained.
| Gross sale proceeds | £745,000 |
| Purchase price | £525,000 |
| Purchase costs (SDLT, legal) | £18,200 |
| Capital improvement (2019 loft conversion) | £28,000 |
| Selling costs (estate agent, legal) | £13,400 |
| Adjusted base cost + costs | £584,600 |
| Gross gain | £160,400 |
| Exempt period (60 months occupation + 9 months final) | 69 months |
| Taxable period (114 − 69) | 45 months |
| PRR (69/114 × £160,400) | £97,074 |
| Taxable gain (after PRR) | £63,326 |
| Lettings relief (shared occupation not met) | £0 |
| Less two annual exempt amounts (2 × £3,000) | £6,000 |
| Taxable amount (split 50/50 between owners) | £57,326 |
| CGT @ 24% (higher rate, residential) | £13,758 |
The taxable gain after PRR is £63,326 — CGT of £13,758 split between the two owners, reported within 60 days of completion via HMRC's online service. Had an accountant applied pre-April-2020 lettings relief by reflex (the £40,000-per-owner cap), they would have further reduced the taxable gain to zero and reported no tax — an error of £13,758 plus interest and penalties once spotted. Had the loft conversion not been documented to HMRC's standards (contracted invoices plus Building Control sign-off), the base cost would have been overstated by the same £28,000 × 24% × (45/114) ≈ £2,654 of tax. Neither error is obvious without the specific knowledge that Pinner's accidental-landlord scenario demands.
HA5 client: £11,200 of overclaimed lettings relief reversed before filing
A Pinner couple selling a former-residence-now-let house came to the scheme two weeks after completion, with a 60-day return deadline approaching. Their solicitor's estimate had already been provided to the conveyancer: £0 CGT, on the basis that PRR plus the £40,000-per-owner lettings relief covered the gain entirely. A specialist reviewed the occupancy history within an hour of instruction: the couple had moved out in 2020 and let the property solely to third-party tenants through a letting agent, with no shared occupation at any point. Lettings relief under the post-April-2020 rules did not apply. The corrected 60-day return reported a taxable gain of £48,600 between the two owners and CGT of £11,664 — filed on time, with no late-filing penalty. Had the solicitor's original figure been submitted, HMRC's now-routine cross-check against the rental income history declared on self-assessment would have triggered a compliance review and £1,500–£3,000 of interest and penalty exposure. The specialist fee was £850.
Case study details paraphrased. No identifying information published.
Questions specific to cgt planning in Pinner
I moved out of my Pinner house and rented it out. Does lettings relief reduce my CGT?
How do I prove a capital improvement from five or ten years ago on my HA5 property?
Do I have to report the sale of my Pinner rental within 60 days, even if no tax is due?
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