Interest-Only Mortgage Calculator

Paying the rent on your loan

An interest-only mortgage does exactly what the name says. Each month you pay the interest the lender charges and nothing toward the loan itself. The balance never moves. At the end of the agreed term, the full original amount is still owed in a single lump, the so-called balloon. This calculator shows that trade clearly: a low monthly payment now, set against a debt that is exactly as large at the finish as it was on day one. It is a structure with real uses and a real trap, and the numbers make both obvious.

Who actually uses this in Ireland

For owner-occupiers, fully interest-only mortgages are now rare. Lenders and the Central Bank treat them cautiously, because a borrower builds no equity and faces a large bill they may not be able to clear. Where you do see them is in buy-to-let investing, where a landlord pays only the interest, lets the rent cover it, and plans to repay the capital by eventually selling the property. They also appear as short bridging arrangements, or as a temporary forbearance measure when a household hits financial trouble and the lender agrees to interest-only for a spell.

If you are an investor, note that mortgage interest on a rental is generally deductible against rental profit, which changes the after-tax cost of an interest-only loan in a way an owner-occupier never sees. That is a separate calculation, but it is part of why the structure persists on the investment side. By keeping the monthly outgoing low and fully deductible, a landlord can hold a property through quiet years and bank on the eventual sale to repay the capital, accepting that the gain on disposal will face Capital Gains Tax at 33 percent.

€300,000 at 4 percent for five years

Take a €300,000 loan at a 4 percent rate on a five year interest-only period. The annual interest is 4 percent of €300,000, which is €12,000, so the monthly payment is €1,000. Over five years that is €60,000 of interest paid. And the balloon still owed at the end is the entire €300,000, untouched.

You will have handed the lender €60,000 and reduced the debt by zero. A capital and interest mortgage on the same terms would cost more each month but would chip the balance down steadily, so by year five you would owe noticeably less. The €60,000 here buys you time and lower payments, not ownership.

The plan for the balloon is everything

An interest-only loan is only as safe as your strategy to clear the lump at the end. The credible exits are simple to list: sell the asset, refinance onto a repayment mortgage, or have a separate savings or investment pot maturing to settle it. The common mistake is to enjoy the low payments for years with no real plan, then arrive at the term end unable to refinance because rates have moved or income has fallen. Before you take interest-only, write down exactly how the €300,000 gets repaid. If you cannot, the structure is not for you.

Can I overpay an interest-only mortgage to reduce the balloon?

Often yes, if the lender allows capital overpayments. Any amount you pay above the interest goes directly against the balance and shrinks the final lump. Check for early repayment charges first, which are more common on fixed rates than on trackers or variable rates.

Why is my real cost higher than the interest shown?

Because this tool counts only the interest you pay during the term. It does not include what it costs to actually clear the €300,000 balloon later, whether through years of saving or a new mortgage. Add that repayment plan to see the true lifetime cost of the borrowing.