UK Interest-Only Mortgage Calculator (2026)

Outstanding balance, property value, interest rate, years remaining.

Existing savings earmarked for repayment, and how much you can contribute monthly.

Regional CAGR drives property projection. Age matters for lender age-at-term-end rules.

Cash ISA (4.5%), S&S ISA (6%), Pension (6.5% + tax relief), Overpayment (at mortgage rate).

See 3 scenarios (pessimistic/base/optimistic) and 4 strategies (savings/switch/part-and-part/downsize).

If shortfall flagged or FCA review triggered, start a lender conversation within the next month.

Endowment-backed IO mortgages sold 1988–2000 frequently under-performed. If you were mis-sold (e.g. adviser didn't explain shortfall risk, endowment "guaranteed" to cover mortgage, no repayment alternative offered), you can complain to the Financial Ombudsman Service — up to 6 years after the advice (or 3 years after you reasonably ought to have known about the shortfall). Compensation based on lost returns vs a safer repayment alternative. Still £millions paid annually in endowment claims — worth investigating old paperwork.

Most UK lenders require the mortgage to be repaid by borrower age 70–75 (some 80). If you'd be 73 at term end and want to extend/remortgage, options shrink. Specialist later-life lenders (Retirement Advantage, Legal & General Home Finance, Livemore) offer products for borrowers aged 55–80 specifically — interest rates higher (5.5–8%) but available. Independent mortgage broker with later-life specialism (e.g. Key Later Life Finance) essential.

Using pension tax-free lump sum (PCLS — 25% of pot, max £268,275) to clear IO mortgage at age 55+. Attractive because: tax-free, no market exposure post-drawdown. Risks: (1) Shrinks retirement income substantially. (2) If pot is invested, market crash near retirement reduces available lump sum. (3) Pension access age rises to 57 from April 2028 (for most). Stress-test with a pension calculator — clearing £200k mortgage means losing £10k/yr retirement income (at 5% withdrawal rate).

Lifetime mortgage interest rolls up — £100k borrowed at 6.5% doubles in 11 years, triples in 17. For a 60-year-old with 20+ year life expectancy, equity release can consume most of the property value. Modern plans include: (1) Fixed early-repayment charges (not gilt-linked). (2) Inheritance guarantees (protects a minimum %). (3) Drawdown facilities (pay interest only on what you take). Always consult ERC-member adviser. Cost: 6–8% advice fees + 7%+ APR. Last resort only after exploring downsize and savings plan.