Self-storage looks simple: a landlord builds or converts a building, divides it into units and lets them to households and small businesses. For Safestore (LSE:SAFE) and Big Yellow (LSE:BYG), both FTSE 250 constituents, the numbers that matter most are how much of that space is let and at what price.

That is why occupancy sits at the heart of both companies' updates. A storage store carries largely fixed costs, so once it passes break-even occupancy, much of each additional pound of rent flows through to profit. Small changes in the share of space let can therefore move Earnings noticeably.

In 2026 both groups are lifting rents while like-for-like occupancy drifts slightly lower, and both are opening stores that start almost empty. This explainer draws on the companies' own announcements.

How self-storage earns its keep

Operators report occupancy as the share of lettable space that is let. Revenue is broadly occupancy multiplied by average rent per square foot, plus ancillary income such as insurance. The two levers can pull against each other: pushing rates can slow lettings, while discounting to Fill space dilutes rent.

Definitions also differ. Big Yellow quotes occupancy against maximum lettable area (MLA), the full capacity of its stores. Safestore's quarterly occupancy is quoted against current lettable area (CLA), which excludes space not yet fitted out. The two companies' percentages are therefore not strictly comparable; trends are more informative than levels.

Safestore: a UK leader with a European spread

Safestore Holdings describes itself as the UK's largest self-storage group. At 31 July 2026 it operated 216 stores, including 141 in the UK and 36 in the Paris region, with the rest in Spain, the Netherlands, Belgium and joint ventures in Germany and Italy. Its financial year ends on 31 October.

Its third-quarter trading update, published on 3 September 2026, showed group revenue for the three months to 31 July up 4.4% to £62.2m, or 4.1% at constant exchange rates (CER), which strips out currency effects on euro income. Like-for-like revenue rose 1.9% at CER: up 1.9% in the UK, down 2.5% in Paris and up 11.6% in the newer "expansion markets".

Occupancy moved the other way. Like-for-like closing occupancy was 79.6% of CLA, down 0.8 percentage points year on year, while the like-for-like average storage rate rose 3.4% to £31.29 per sq ft. Management guided that adjusted diluted EPRA Earnings Per Share for the 2026 financial year would land in the lower half of the analyst range of 39.6p to 42.4p, and said it was reviewing the phasing of its 2027–28 UK pipeline.

The Balance Sheet carries more Debt than Big Yellow's. Safestore's interim results for the six months to 30 April 2026 showed a Loan-to-Value (LTV) Ratio of 29.1%, net debt of £1,100.8m and EPRA net tangible assets (NTA), a standard measure of underlying net asset value, of 1,120p per share. The Interim Dividend was raised to 10.2p from 10.1p.

Big Yellow: London focus, low leverage

Big Yellow Group operates 113 stores concentrated in London and the South East, and its financial year ends on 31 March. Its results for the year to 31 March 2026 showed revenue up 2% to £209.1m, adjusted earnings per share up 2% to 59.0p and a full-year dividend of 47.2p. EPRA NTA was 1,370.4p per share and LTV just 15%, with net debt of £476.7m.

Occupancy is again the pressure point. Total closing occupancy at 31 March 2026 was 74.2%, against 78.7% a year earlier, diluted by new capacity; like-for-like occupancy fell 1.7 points to 77.0%. Average net achieved rent rose 4% to £35.98 per sq ft.

The first-quarter trading statement of 20 July 2026 described a "resilient" performance. For the quarter to 30 June, revenue rose 3% to £53.2m, like-for-like closing occupancy was 79.2% (down 0.2 points year on year) and closing net achieved rent rose 2% to £36.45 per sq ft. The pipeline comprises 12 stores, with openings scheduled at Staples Corner, Kentish Town, Epsom and Wapping during 2026.

Big Yellow is also recycling non-storage assets. It sold its Harrow industrial estate for £38.4m in June 2026, and its announcement record shows further disposals of industrial estates at Staines and Bracknell in September 2026.

Its recent corporate history is relevant too. After Blackstone said on 13 October 2025 that it was considering a possible cash offer, Big Yellow's board ended discussions on 4 December 2025, finding "no basis for continuing discussions". The next day Blackstone confirmed it was not intending to make an offer. No subsequent offer approach appears in the company's announcements.

Comparing the two occupancy stories

On our reading, the two companies are telling similar stories through different portfolios: pricing up, like-for-like occupancy slightly down, and new stores diluting headline occupancy while they fill.

Safestore's European spread supplies growth, particularly in its expansion markets, but also exposes it to Paris, where management cited a subdued economic backdrop and new stores drawing enquiries from existing ones. Its higher Leverage means financing costs weigh more heavily on earnings.

Big Yellow's low LTV gives it balance-sheet capacity, while its concentration ties results to one regional economy. On our calculation, its 2026 dividend of 47.2p was covered about 1.25 times by adjusted earnings of 59.0p.

Risks and items to monitor

The main risks are shared. A weaker housing market means fewer moves and less storage demand. Rising Business rates, energy and staff costs pressure margins, and interest rates affect both debt costs and valuations.

Safestore's full-year results for the year to 31 October 2026 are its next major reference point; last year's were published on 15 January 2026. For Big Yellow, interim results for the six months to 30 September 2026 should show whether like-for-like occupancy stabilises as its new London stores open.

Why occupancy remains the headline number

Occupancy is not the only measure that matters, but it links most directly to Operating Leverage in self-storage. When occupancy rises alongside firm rents, earnings tend to benefit disproportionately; when it slips, rate increases have to do all the work.

Safestore (LSE:SAFE) is balancing European expansion with heavier borrowing; Big Yellow (LSE:BYG) is filling new London stores from a less indebted balance sheet. For both, the next occupancy figure will say more about earnings momentum than any other single number.