Interest-Only vs Repayment Mortgages for Buy-to-Let
2026-06-14
This is the question that divides the property investment community more than almost any other. Interest-only maximises cashflow today. Repayment builds equity and eliminates debt over time. Both have legitimate use cases, and the right answer depends on where you are in your investment journey.
The Basic Difference
Interest-only: You pay only the interest each month. The loan balance stays the same for the entire term. At the end (typically 25 years), you still owe the full amount and must repay it — usually by selling or remortgaging.
Repayment (capital + interest): You pay the interest plus a portion of the principal each month. The loan balance reduces over time and reaches zero at the end of the term. You own the property outright.
The Numbers Side by Side
Property: £200,000 | Mortgage: £150,000 (75% LTV) | Rate: 5.0% | Term: 25 years
| Interest-Only | Repayment | |
|---|---|---|
| Monthly payment | £625 | £877 |
| Annual cost | £7,500 | £10,524 |
| Monthly cashflow (rent £1,000) | £375 surplus | £123 surplus |
| Total interest paid over 25 years | £187,500 | £113,100 |
| Balance remaining after 25 years | £150,000 | £0 |
| Equity at year 25 (no growth) | £50,000 | £200,000 |
:::stats £252/mo | Extra Cost of Repayment £150,000 | Debt Still Owed on IO After 25 Years £74,400 | Interest Saved Over Full Term (Repayment) :::
The monthly difference is £252. Over a year, that's £3,024 less cashflow on repayment. Over 25 years, repayment costs you £75,600 more in total payments — but saves you £74,400 in total interest AND you own the property outright.
:::tool mortgage-calculator Compare Both Options for Your Deal :::
The Case for Interest-Only
1. Cashflow is King (During Acquisition)
When you're building a portfolio, every pound of cashflow matters. The £252/month saving on interest-only translates to £3,024/year per property. Across 5 properties, that's £15,120 more cash in your pocket annually — capital you can save towards the next deposit.
2. Tax Efficiency (Sort Of)
Under Section 24, mortgage interest gets a 20% tax credit regardless of whether you're on interest-only or repayment. But with repayment, the capital portion of your payment isn't deductible at all — it's not interest, it's repaying debt. You get no tax benefit from the repayment element.
In a limited company, the full interest is deductible from profits. But again, only the interest portion — not the capital repayment. So repayment costs you more out-of-pocket and provides no additional tax relief.
3. Flexibility
Interest-only gives you options. You can overpay voluntarily when you have surplus cash. You can use the freed-up capital for other investments. You can sell at any time without worrying about early repayment charges eating into equity you've built.
4. Inflation Erodes the Debt
A £150,000 debt today will feel like significantly less in 25 years due to inflation. If inflation averages 3% annually, that £150,000 has the purchasing power of roughly £70,000 in today's terms by 2051. Time degrades the real value of fixed debt.
The Case for Repayment
1. The Endgame Is Clear
At the end of 25 years, you own the property with no debt. The full rent (minus costs) is cashflow. No refinancing risk, no capital repayment hanging over you, no reliance on property prices being high enough to sell and clear the mortgage.
This is the clearest path to retirement from property. Mortgage-free properties generate £6,000-£8,000/year each in net cashflow — enough to replace a salary with 5-10 properties.
2. Forced Discipline
Repayment mortgages force you to build equity whether you feel like it or not. Interest-only requires the discipline to save or invest the difference productively. Many investors choose interest-only with good intentions but spend the "savings" rather than deploying them.
3. Lower Total Cost
Over the full 25-year term, repayment costs £74,400 less in total interest. That's real money. The monthly pain buys long-term savings.
4. Remortgaging Gets Easier Over Time
As you pay down the balance, your LTV drops. Lower LTV = better rates at each remortgage. A property that started at 75% LTV on repayment might be at 50% LTV after 10 years (with capital growth), qualifying you for the cheapest rates available.
On interest-only, your LTV stays at 75% forever (unless the property appreciates). You're permanently in the higher-rate bracket.
5. Less Risk in a Downturn
If property prices fall 20%, a repayment investor who's been paying down for 10 years still has equity. An interest-only investor at 75% LTV is immediately in negative equity. This matters if you need to sell or remortgage during a downturn.
The Hybrid Approach
Many experienced investors use a phased strategy:
Phase 1 (Years 1-10): Interest-only. Maximise cashflow during the acquisition and growth phase. Every property is interest-only, freeing cash for deposits on the next purchase. Build the portfolio to target size.
Phase 2 (Years 10-25): Switch to repayment. Once the portfolio is fully built, switch to repayment on remortgage. Use the now-larger portfolio's combined cashflow to absorb the higher payments. Properties start clearing their debt, one by one reaching mortgage-free status.
Phase 3 (Year 20+): Sell selectively. Use the proceeds from selling 1-2 properties to clear the remaining mortgages on the others. Accelerate the path to a fully unencumbered portfolio.
This approach gives you the cashflow when you need it (during growth) and the debt elimination when you want it (approaching retirement).
Impact on Lender Affordability
Interest-only and repayment are assessed differently by lenders:
Interest-only: Rent must cover 125-145% of the interest payment. Easier to pass because the payment is lower.
Repayment: Some lenders assess on the interest-only payment regardless. Others assess on the actual repayment figure, which is harder to pass. Check with your broker.
If you're tight on affordability (rent barely covers the stress test), interest-only may be your only option at 75% LTV. The Mortgage Calculator shows affordability for both options.
What Happens at the End of an Interest-Only Term?
This is the elephant in the room. After 25 years of interest-only, you still owe £150,000. Your options:
- Remortgage. Extend the mortgage for another term. This works if you're not too old (many lenders cap at age 75-80) and the property still passes affordability.
- Sell the property. Use the sale proceeds to repay the mortgage. Keep the profit (hopefully significant due to capital growth).
- Repay from other sources. Savings, pension lump sum, sale of another asset.
- Switch to repayment. At remortgage, switch to repayment for the remaining years. Monthly payments will be high if the remaining term is short.
The key question: do you have a credible exit strategy? "I'll worry about it in 25 years" is not a strategy. "I'll sell and clear the debt, banking the capital growth" is a strategy — but it assumes the property has grown in value.
The Decision Framework
| Your Situation | Best Choice | Why |
|---|---|---|
| Building a portfolio (first 5-10 years) | Interest-only | Maximise cashflow for deposits |
| Single property, long-term hold | Repayment | Clear it, own it, cashflow it forever |
| Higher-rate taxpayer, personal name | Interest-only | No tax benefit from repayment element |
| Limited company, long hold | Either | Full interest deduction either way |
| Approaching retirement (10-15 years) | Repayment | Eliminate debt before income stops |
| Cash-tight, margins thin | Interest-only | Can't absorb the extra £252/month |
| Discipline issues with saving | Repayment | Forces equity building |
Model Your Specific Scenario
The right answer depends on your numbers. The Mortgage Calculator lets you run both options side by side for any deal — showing monthly payments, total interest over the term, and the equity position at any point.
:::tool mortgage-calculator Compare Interest-Only vs Repayment :::
For longer-term modelling (what does the portfolio look like in 15 years under each strategy?), the Cashflow Projection tool models both approaches over time.
:::tool cashflow-projection Project Your Portfolio's Future :::
Summary
- Interest-only: lower payments, more cashflow, but you never clear the debt
- Repayment: higher payments, less cashflow, but you own the property outright in 25 years
- Most portfolio builders start interest-only and switch to repayment once the portfolio is fully built
- There's no universally "right" answer — it depends on your phase, your cashflow, and your exit plan
- Whichever you choose, have a clear answer to "how does the debt get repaid?"
This guide is for educational purposes only and should not be treated as financial advice. Always consult a qualified mortgage broker before making financing decisions.