Lease Extension Calculator UK 2026
Free lease extension cost calculator
Estimate your lease extension premium under the Leasehold Reform, Housing and Urban Development Act 1993. For flats, houses & shared ownership. Enter details below.
Estimated statutory lease extension premium
How is a lease extension calculated? (Statutory formula)
In the UK, a lease extension calculator estimates the premium the leaseholder pays to the freeholder. The core elements are: diminution in value of the landlord's interest (ground rent capitalisation + reversion value) and, if the remaining lease is under 80 years, marriage value (50% split). Our lease extension cost calculator UK uses these principles, aligning with the 1993 Act and rics lease extension calculator methodology. For leases below 80 years, marriage value dramatically increases the cost – especially for short lease extension calculator scenarios (under 50 years).
Since 2026, ground rent reforms and the Leasehold Reform (Ground Rent) Act 2022 have capped ground rents on new leases, but existing leases may still have rising ground rent. Our tool also handles lease extension calculator rising ground rent by capitalising current payments. For shared ownership lease extension calculator, the valuation is often more complex; we apply a standard adjustment.
Key factors that influence premium:
- Remaining term: The shorter the lease, the higher the premium (marriage value). Lease extension calculator under 50 years often shows costs exceeding 30% of property value.
- Ground rent: Higher ground rent increases the freeholder's interest value, adding cost.
- Property value: Higher value flats lead to higher reversion and marriage value.
- Share of freehold: If you own a share, you can often extend informally with reduced costs (our calculator applies ~20% reduction).
| Lease remaining | Estimated premium range | Marriage value impact |
|---|---|---|
| 85 years | £5,500 – £9,000 | No marriage value |
| 78 years | £11,000 – £17,500 | Moderate (marriage value applies) |
| 68 years | £21,000 – £29,000 | High marriage value |
| 45 years (under 50) | £48,000 – £68,000 | Extremely high premium |
Pro tip: Use the government lease extension calculator as guidance but remember the leasehold advisory service lease extension calculator gives more accurate statutory guidance. Our tool reflects the lease extension calculation formula widely accepted by valuers.
Step-by-step: how to calculate lease extension cost
Market value with a long lease (90+ years).
From your lease document.
Typically 5% for ground rent income.
50% of the increase in property value after extension.
For those asking “how do you calculate a lease extension” – the statutory process requires a Section 42 notice. The lease extension premium calculator we provide gives you an immediate estimate, but a formal RICS valuation is needed for the final figure. This free lease extension calculator helps you budget and negotiate better.
2026 updates: new marriage value thresholds & tax tips
As of 2026, UK property tribunals are applying stricter scrutiny to marriage value calculations. If your lease has between 70 and 80 years, the premium can be negotiated. Our lease extension calculator 2026 incorporates updated deferment rates (4.75%) and capitalisation rates suggested by the Leasehold Advisory Service. Additionally, the lease extension stamp duty calculator note: the premium paid for a lease extension may be liable for Stamp Duty Land Tax (SDLT) if it exceeds £40,000. Always factor that in when budgeting.
For flats with share of freehold lease extension calculator, you can often extend informally (without statutory fees), saving thousands. Our calculator includes that discount. For those searching "lease extension calculator doubling ground rent", be aware that escalating ground rents increase the premium dramatically – you may want to consider a statutory lease extension to revert ground rent to a peppercorn.
- ✅ Extend before lease falls below 80 years to avoid marriage value.
- ✅ Use the calculate lease extension premium feature to negotiate with the freeholder.
- ✅ Check if you qualify for a no-cost informal extension with share of freehold.
- ✅ For shared ownership, speak to your housing association – our tool gives indicative figures.
Lease extension calculator FAQ
Marriage value is the increase in the property's value after granting a longer lease. It applies when the remaining lease is < 80 years and is shared 50/50 between leaseholder and freeholder. Our statutory lease extension calculator includes this automatically.
Yes, but the lease extension calculator under 50 years will show a high premium because marriage value dominates. Act quickly to avoid even higher costs.
It provides a reliable estimate based on statutory valuation principles. However, a qualified surveyor must provide the final figure for the Section 42 process. We update for 2026 interest rates and RICS guidance.
Statutory gives you a 90-year extension at a peppercorn ground rent. Informal is a private agreement. Use our informal lease extension calculator option by checking "share of freehold" where applicable.
This tool is designed for residential flats and houses. Commercial lease extension calculator uses different valuation methods; consult a specialist.
Our tool capitalises current ground rent. If ground rent doubles every 10–15 years, the premium rises substantially; a statutory extension will eliminate future ground rent.