Home loan repayments and total interest.
Monthly repayment
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Total interest
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Total repaid
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Your breakdown
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Worked example
Take a 320,000 euro mortgage at a 4% annual rate over a 30 year term. The monthly rate is 4% divided by 12, and there are 360 monthly payments. Running these through the standard repayment formula gives a monthly payment of about 1,527.73 euro. Over the full 30 years you repay roughly 549,982 euro in total, of which 320,000 is the original loan and about 229,982 euro is interest. In other words the interest alone is close to 72% of the amount borrowed, which is why the term and rate matter so much. Shortening the term or overpaying early cuts the interest sharply.
How it is calculated
A repayment mortgage uses the standard annuity formula, where the monthly payment is the loan multiplied by the monthly rate and a compounding factor over the number of months. Each payment covers the interest accrued that month first, with the rest reducing the balance, so early payments are mostly interest and later ones mostly capital. The monthly rate is the annual rate divided by 12, and the number of payments is the term in years times 12. Total interest is simply the sum of all payments less the original loan. In Ireland the Central Bank mortgage measures cap most lending at 3.5 to 4 times income and 90% loan to value for first time buyers, so affordability often sets the loan size before the rate does. Always compare the APRC rather than the headline rate, since it folds in fees.