Interest-Only Loan Calculator.

Interest-only loans look cheaper because the debt does not move

An interest-only payment is lower for a simple reason: you are not paying the balance down. The monthly number can look attractive, but the structure has not become cheap. It has become deferred. At the end of the interest-only period, the original principal is still there waiting to be repaid.

This calculator is useful because it keeps that hidden part visible. It shows:

• the monthly interest-only payment,
• the total interest paid over the period,
• the principal still due at the end.

That final balance is the number people most need to keep in view.

Where this kind of loan appears

Buy-to-let and investment property

Interest-only is common where the planned exit is sale, refinance, or some other future capital event rather than gradual repayment from income.

Temporary cash-flow pressure

Some borrowers consider interest-only because it reduces the monthly outflow for a period. That can be rational, but only if the repayment route at the end is real rather than assumed.

Comparing structures

Sometimes the right question is not “can I get an interest-only loan?” but “what exactly am I buying with the lower monthly payment?”

A clearer way to compare it

Take the same borrowing amount and compare:

• standard repayment loan,
• interest-only loan,
• the monthly difference,
• the balance remaining at the end.

That side-by-side view is often more revealing than the interest-only calculation alone.

Worked examples

Buy-to-let cash flow

Borrowing 200,000 at 5% interest-only produces a payment of about 833 a month. That may suit the rental cash flow, but it does not reduce the 200,000 balance that still has to be cleared later.

The cost of the “cheaper” payment

On the same borrowing, a 25-year repayment mortgage is roughly 1,169 a month. The gap of around 336 a month is real, but it is not free money. It is the price of leaving the capital outstanding.

A bridging period

If you expect a known future lump sum, interest-only can be a deliberate bridge rather than a long-term strategy. In that case the key number is the total interest paid while you wait.

The question that matters most

How will the balance be repaid at the end?

Not “probably”. Not “if the market is good”. Not “if things improve”.

The entire usefulness of an interest-only calculation depends on whether the exit plan is credible. That might be sale proceeds, investments, bonus income, or refinance capacity, but it has to be concrete enough to test against the final-balance figure.

What this tool does not do

This tool models the interest-only phase only. It does not estimate investment growth, guarantee refinance options, price in fees, or judge suitability. It also does not remove the need for proper advice when the amounts are large or the exit route is uncertain.

Better ways to use the result

• Compare it directly with a repayment loan for the same amount.
• Treat the monthly saving as borrowed breathing room, not as evidence the loan is cheap.
• Revisit the numbers when rates change; interest-only payments are highly sensitive to rate increases.
• Write down the end-of-term repayment plan and compare it with the actual balance, not with a vague target.