Leasehold Extension Calculator
Estimate lease extension premium including marriage value, ground rent and professional fees.
Last updated: April 2026 · Source: GOV.UK — Extending your leasehold
Under 80 years — marriage value applies!
Estimated Total Cost
£61,450.00
Premium: £57,750.00 + fees: £3,700.00
Value Uplift After Extension
+£57,647.06
Property worth £407,647.06 with extended lease
| Diminution in reversion | £26,250.00 |
| Capitalised ground rent | £7,000.00 |
| Marriage value (50%) | £24,500.00 |
| Premium | £57,750.00 |
| Surveyor / Valuer | £700.00 |
| Legal Fees (yours) | £1,500.00 |
| Landlord's Costs | £1,500.00 |
Current relativity: 85% of freehold value. Under 80 years: marriage value applies, increasing the premium significantly. Extend before it drops below 80!
Disclaimer
This calculator is provided for informational purposes only and should not be considered as financial or tax advice. All calculations are performed locally in your browser — no personal data is collected or sent to our servers. Rates and thresholds are sourced from HMRC and GOV.UK and are updated for the current tax year. Always verify results with HMRC or consult a qualified professional before making financial decisions.
How It Works
The cost of extending a leasehold property lease is calculated using a statutory valuation method set out in the Leasehold Reform, Housing and Urban Development Act 1993. The premium has three components: the landlord's loss of ground rent for the remaining term, the landlord's loss of the reversion (the property value they would receive when the lease expires), and 50% of the "marriage value" (the increase in property value created by the extension).
Marriage value only applies when the unexpired lease is below 80 years — this is why it is generally advised to extend before the lease drops below 80 years, as the cost increases significantly. The capitalisation rate (typically 6-8%) and the deferment rate (typically 5% as set by the Sportelli ruling) are key assumptions in the calculation.
Under the Leasehold and Freehold Reform Act 2024, planned changes may remove marriage value from the calculation entirely. This calculator uses the current statutory method and shows the estimated premium, broken down by component. Results are indicative — a formal RICS surveyor valuation may differ.
Example: Flat worth £350,000, 72 years remaining, £200/year ground rent
- Ground rent loss (capitalised): approx. £3,100
- Reversion loss (value of freehold in 72 years): approx. £11,200
- Marriage value (50% of uplift): approx. £8,500
- Total estimated premium: approx. £22,800
- With 82 years remaining (no marriage value): approx. £12,000
Frequently Asked Questions
- What does the Leasehold Extension Calculator do?
- Estimate lease extension premium including marriage value, ground rent and professional fees. All calculations are performed in your browser using official UK rates and thresholds.
- Is this based on current interest rates?
- You can enter any interest rate to model different scenarios. Check the Bank of England base rate and current mortgage deals from lenders for the latest rates.
- Should I get professional advice?
- This calculator provides estimates for guidance only. For a formal mortgage offer, speak to a mortgage broker or lender who can assess your full circumstances and provide personalised advice.