Interest only vs repayment mortgage: which fits you?

The difference between an interest only vs repayment mortgage is what your monthly payment covers. With a repayment (capital-and-interest) mortgage, each payment covers interest and gradually pays off the loan, so you owe nothing at the end. With an interest-only mortgage, you pay only the interest, the payment is lower, and the full loan is still outstanding at the end of the term.

Neither type is automatically better. Interest only buys lower monthly costs and more flexibility at the price of higher lifetime interest and a large lump sum due later. Repayment costs more each month but steadily removes debt and risk. The numbers below make the trade-off concrete.

All examples use euros and a hypothetical interest rate of 4% per year. This is an illustration, not a market rate; the maths works the same in any currency.

How each mortgage type works

Repayment mortgage

The lender sets a fixed monthly payment using the annuity formula, so that the loan reaches zero at the end of the term. Early payments are mostly interest, later ones mostly principal. If you want the mechanics in detail, see how mortgage amortization works.

Interest-only mortgage

The monthly payment is simply:

Monthly payment = loan × annual rate ÷ 12

The balance never moves (unless you overpay). At the end of the term you repay the full amount in one go, from whatever repayment strategy you agreed with the lender.

Part-and-part

Some lenders let you split the loan: one part on repayment, one part interest only. This sits between the two extremes and is worth knowing about if neither pure option fits.

Interest only vs repayment mortgage: €200,000 over 25 years

Loan of €200,000, term 25 years, hypothetical 4% fixed for the whole term:

	Repayment	Interest only	Part-and-part (50/50)
Monthly payment	€1,055.67	€666.67	€861.17
Payments per year	€12,668	€8,000	€10,334
Total interest over 25 years	€116,702	€200,000	€158,351
Debt left at the end	€0	€200,000	€100,000

How these figures are calculated:

• Repayment: annuity formula M = P × i ÷ (1 − (1 + i)^−n), with i = 0.04 ÷ 12 and n = 300, gives €1,055.67.
• Interest only: €200,000 × 0.04 ÷ 12 = €666.67. Over 300 months that is €200,000 of interest, and the €200,000 loan is still owed.
• Part-and-part: €100,000 interest only (€333.33) plus €100,000 on repayment (€527.84) = €861.17 a month.

The interest-only borrower pays €389 a month less but, after 25 years, has paid about €83,000 more interest and still owes the full loan. You can run your own figures in the mortgage calculator, which handles both repayment and interest-only loans.

The "invest the difference" argument

A common case for interest only is: take the lower payment, invest the €389 a month you save, and use the investment pot to repay the loan at the end. Whether that works depends on the return you earn after costs and tax, compared with the mortgage rate.

Investing €389.01 a month for 25 years, at hypothetical constant net returns:

Hypothetical net return	Pot after 25 years	Compared with the €200,000 debt
3%	about €173,500	about €26,500 short
4% (same as mortgage rate)	about €200,000	exactly enough
5%	about €231,700	about €31,700 surplus

This is no coincidence. When your net return equals the mortgage rate, the two approaches come out identical. Interest only plus investing only wins if you reliably earn more than the mortgage rate after fees and tax, and you never dip into the pot. Real returns are not constant, can be negative for years and may fall just before the loan is due. The mortgage interest, on the other hand, is certain.

For an investment property, the "investment" is often the property itself: the plan is to sell or refinance at the end. That works if the property holds its value and lenders still offer suitable loans at that time, neither of which is guaranteed.

Monthly cash flow on a rental property

For landlords, the monthly difference changes the picture significantly. Suppose a property rents for €1,200 a month and running costs (management, insurance, maintenance, non-recoverable service charges, vacancy allowance) average €400 a month. That leaves €800 before financing.

	Repayment	Interest only
Rent minus running costs	€800	€800
Mortgage payment	€1,056	€667
Monthly cash flow	−€256	+€133
Debt repaid in month one	€389	€0

On repayment, you top up €256 a month from your own pocket, but €389 of the payment is building equity. On interest only, the property pays for itself, but your debt stays flat. Both are valid positions; what matters is that you know which one you are in. The article on rental property cash flow goes deeper, and the rental yield calculator shows monthly cash flow for your own figures.

Sensitivity to interest-rate rises

If your rate is variable or your fixed period ends, payments are recalculated. Interest-only payments react more strongly in percentage terms, because the whole payment is interest.

Hypothetical rate	Repayment (25 years)	Interest only
4%	€1,055.67	€666.67
6%	€1,288.60	€1,000.00
Increase	+22%	+50%

A landlord whose cash flow is only slightly positive on interest only can be pushed into negative territory quickly. Stress test your plan at clearly higher rates before you commit.

Pros and cons at a glance

Repayment mortgage

• Debt falls to zero by the end of the term.
• Lower total interest for the same rate and term.
• Your loan to value falls every month, which can help when refinancing. See loan to value ratio explained.
• Higher monthly payment, which reduces cash flow and can make affordability tests harder.

Interest-only mortgage

• Lower monthly payment and stronger monthly cash flow.
• More flexibility to hold cash reserves or invest elsewhere.
• Higher total interest, and the full loan is due at the end.
• Your equity depends entirely on property values and any separate savings.
• Lenders usually require a credible repayment strategy, and some restrict interest-only lending for owner-occupiers. Rules and availability vary by country and lender.

When each option tends to make sense

Repayment is usually the default choice for a home you live in, for anyone without a clear and robust exit plan, and for investors who want debt to fall over time and reduce risk as they approach retirement.

Interest only can make sense for experienced investors who treat the loan as long-term leverage, hold healthy cash reserves, have a realistic exit (sale, refinance or savings) and understand they are taking more risk. It is also used for short holding periods where little principal would be repaid anyway.

Part-and-part suits borrowers who want some debt reduction while keeping payments manageable.

Whatever you choose, discuss it with a qualified mortgage adviser. Regulation, lender criteria and the tax treatment of mortgage interest for landlords differ widely between countries; a tax adviser can explain how interest and principal are treated where you are.

Common mistakes

• Choosing interest only for affordability alone. If you can only afford the property on interest only, you may not be able to afford the debt at the end either.
• No written repayment plan. "I will sell" or "I will refinance" is a plan only if the numbers still work in a weaker market.
• Assuming investment returns will beat the mortgage rate. They might, but the gap must cover fees, tax and bad years.
• Spending the monthly saving. The interest-only advantage disappears if the difference is not saved or put to productive use.
• Ignoring rate rises. Interest-only payments rise faster in percentage terms when rates go up.
• Forgetting to review. Revisit the decision whenever your fixed period ends, your income changes or the property's value moves.

Key takeaways

• Repayment: higher monthly cost, lower total interest, zero debt at the end.
• Interest only: lower monthly cost, higher total interest, full debt at the end.
• In the example, interest only saves €389 a month but costs about €83,000 more interest and leaves €200,000 owing.
• Investing the difference only wins if your net return beats the mortgage rate consistently.
• For landlords, interest only improves cash flow but shifts all equity growth onto the property's value. Run both scenarios in the mortgage calculator and read the buy to let investing guide before deciding.