There are a great many pages, ours included, explaining how Section 24 works. There are very few counting what landlords actually did about it. This one does only the second thing. Every figure below comes from our own count of the Companies House register, published as the UK SPV Incorporation Index, and the headline is simple: incorporations on SIC 68209, the buy to let SPV code, went from 19,733 in 2016 to 69,039 in 2025. That is 3.5 times the starting level, a rise of 249.9 per cent.
If you need the mechanism rather than the measurement, the Section 24 pillar and its cluster cover it in full, including the mortgage interest restriction guide and the detailed finance costs guide. This page assumes you already know what the rule does and asks a different question: what shows up on the register.
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Landlord incorporations, 2016 to 2025
The table below is the whole story in one place. The headline column is SIC 68209 alone. The union column is the deduplicated count across all four property codes in the index (68100, 68201, 68209 and 68320), which includes developers, letting agents and housing association letting alongside the SPVs. The phase in column marks the tax years in which the Section 24 restriction was being introduced, from 2017/18 through to 2020/21, fully in force from April 2020.
| Year | SIC 68209 (headline) | Union series (4 codes) | Year on year, 68209 | Section 24 status |
|---|---|---|---|---|
| 2016 | 19,733 | 33,040 | baseline | Announced, not yet in force |
| 2017 | 27,014 | 43,422 | +36.9% | Phase in year 1 (2017/18) |
| 2018 | 29,736 | 46,465 | +10.1% | Phase in year 2 (2018/19) |
| 2019 | 36,719 | 54,638 | +23.5% | Phase in year 3 (2019/20) |
| 2020 | 45,802 | 66,575 | +24.7% | Phase in year 4, fully in force April 2020 |
| 2021 | 50,689 | 70,926 | +10.7% | Fully in force |
| 2022 | 51,938 | 72,279 | +2.5% | Fully in force |
| 2023 | 52,950 | 74,639 | +2.0% | Fully in force |
| 2024 | 64,583 | 89,857 | +22.0% | Fully in force |
| 2025 | 69,039 | 95,140 | +6.9% | Fully in force |
Source: UK SPV Incorporation Index, our count of Companies House Advanced Search data, calendar years 2016 to 2025, published under the Open Government Licence v3.0. Percentages are our calculation from the annual counts above.
Reading the shape, not just the total
Three things stand out once the years are lined up.
First, the step is immediate. The largest proportional jump in the entire ten year series is 2017, at 36.9 per cent, and 2017/18 is the first tax year of the phase in. Nothing later in the series matches that rate of increase. Whatever else was happening in the market, the register moved in the first year the rule started to bite, not at the end of it.
Second, the growth did not stop when the phase in did. The restriction has been fully in force since April 2020, and the count rose in every year afterwards. Between 2020 and 2025 the headline series added a further 23,237 companies, more than the entire 2016 annual total. A one off adjustment to a rule change would have flattened. This did not.
Third, there is a distinct second surge that has nothing to do with the phase in at all. After three quiet years (2021 to 2023 averaged growth of 5.1 per cent) the count jumped 22.0 per cent in 2024, an absolute addition of 11,633 companies, the largest single year addition in the series. By then Section 24 had been fully in force for four years. Something else drove 2024, and honest reading of the register means saying so rather than attributing every movement to one statute.
The headline series grew faster than the sector around it
The union series is a useful control. It contains the same landlord SPVs plus developers, agents and housing association letting, all of which faced the same interest rates, the same house prices and the same economy, but not Section 24, which restricts finance cost relief for individual landlords of residential property. Over the decade the union series rose 188.0 per cent, from 33,040 to 95,140. The headline series rose 249.9 per cent. The specifically landlord shaped code outgrew the broader property register by a clear margin, which is the closest thing to a natural comparison the register offers.
It is not proof of causation, and we are not going to dress it up as such. Company formation is a decision with several inputs, and a count of the register records the outcome, not the reasoning. What it does establish is scale and timing, which is more than most commentary on this subject offers.
The after story: a record year, then a turn
Calendar 2025 is the peak of the series at 69,039, and the single strongest month in our monthly data is September 2025 at 6,672 incorporations on SIC 68209. That is where the growth narrative ends.
On settled data, the first half of 2026 recorded 32,441 incorporations on SIC 68209, against 35,168 in the first half of 2025, a fall of 7.8 per cent. The union series fell further, 9.7 per cent, from 48,826 to 44,076. June 2026 alone came in at 4,840, down 20.1 per cent on June 2025. The trailing twelve months to June 2026 stand at 66,312, below the 69,039 calendar 2025 total, so the annual line has begun to bend as well as the monthly one.
| Measure (SIC 68209) | 2025 | 2026 | Change |
|---|---|---|---|
| First half, January to June | 35,168 | 32,441 | -7.8% |
| June alone | 6,054 | 4,840 | -20.1% |
| Union series, first half | 48,826 | 44,076 | -9.7% |
Our figures, from monthly Index data settled to June 2026. The two months after June exist in the underlying series but are provisional and are excluded here, because recent months fill in as companies are registered and classified. A provisional month read as final always understates the count, which is the single most common error in reporting this data.
The correct reading of that turn is deceleration from a record base, not collapse. A first half of 32,441 still annualises to a level roughly three times the whole of 2016. The rate of new company formation has come off a peak; the stock of landlord companies built over the decade has not gone anywhere. Netting dissolutions off the formation count confirms it, and that arithmetic is set out in are landlords really leaving. What happens next is a question the monthly series will answer month by month, and we publish it rather than forecast it.
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Two dates the register has not seen yet
Two tax changes sit ahead of the settled data, and both are named here only so the timeline is complete. Neither is analysed on this page.
From April 2026, incorporation relief under section 162 TCGA 1992 became a mandatory positive claim rather than relief that applied automatically where the conditions were met. It was not withdrawn, despite a fair amount of circulating commentary saying so. The mechanics of the claim belong on our section 162 incorporation relief guide.
From April 2027, property income tax rates rise by 2 percentage points, to 22, 42 and 47 per cent. The mortgage interest reducer rises from 20 to 22 per cent at the same time, which is the offset to the basic rate change rather than a separate squeeze. What that means for a given portfolio is worked through on the 2027 rates and the incorporation decision page, and the practical steps sit in our guide to incorporating a property portfolio. If you are weighing the structure itself rather than the history, start at the SPV company hub.
Whether either date leaves a mark on the register is not something we are going to guess at. It is something the monthly count will show, once the relevant months settle.
How these figures are built
Every number on this page is a direct count of companies incorporated at Companies House, filtered by SIC code and incorporation month through the Advanced Search API, under the Open Government Licence v3.0. The full method, including the known weaknesses, is set out in our published methodology for the UK SPV Incorporation Index. Two points from it matter when reading this page.
The SIC code is self declared at incorporation, so the count measures how companies describe themselves, not a verified assessment of what they go on to do. And a calendar year count never lines up exactly with a tax year rule, so the phase in column in the first table is an overlay for orientation, not a claim that the two grids match. The live series, updated monthly, is on the UK SPV Incorporation Index.