Ireland Calculator Methodology
Last updated 27 July 2026
Every Ireland calculator on Fiscalgrove is built from a documented formula and the specific lending or statutory data that applies to it. This page summarises the shared method; each calculator's own page also works through its formula and an Irish example in context. This section grows as each calculator ships.
Annuity repayments
An Irish repayment mortgage is a standard annuity (reducing-balance) loan: each repayment covers the interest charged since the last payment, and the rest reduces the principal. The payment is the textbook reducing-balance formula, M = P × r × (1+r)^n ÷ ((1+r)^n − 1), where P is the loan amount, r is the annual rate divided by the number of payments a year, and n is the total number of payments. We compute on full unrounded figures and only round to the cent for display, so the schedule does not drift.
Rate convention
Ireland quotes a nominal annual rate with ordinary monthly compounding, so the periodic rate is simply the annual rate divided by the number of payments a year. There is no semi-annual convention as in Canada, so the rate you enter is applied directly.
Repayment frequency
Each frequency is modelled as a genuine schedule on that basis (52, 26, or 12 payments a year), rather than halving or quartering the monthly figure. Paying more often lowers total interest slightly, because the balance falls sooner. The headline figure is the payment for your chosen frequency, with a monthly-equivalent alongside so options compare like for like.
Editable defaults and statutory limits
Every default in a calculation is visible and editable in the calculator itself. Where a figure is set by regulation, such as the Central Bank of Ireland loan-to-income and loan-to-value mortgage measures, it reflects the published rule as at the verification date shown, and is not applied silently inside the repayment maths.