Compound Interest Calculator
See the power of compound interest on your savings or investments. Enter your starting amount, interest rate, and how long you plan to invest to see your projected final value. Add regular monthly contributions to see how consistent saving accelerates growth.
How is this calculated?
This calculator uses the standard compound interest formula. For a lump sum: FV = P × (1 + r/n)^(n×t), where P is the principal, r is the annual rate, n is the number of compounding periods per year, and t is the number of years. For regular contributions, the future value of an ordinary annuity formula is added: PMT × [(1 + r/n)^(n×t) - 1] / (r/n). The effective annual rate (EAR) accounts for the compounding frequency.
Frequently Asked Questions
What is compound interest?
Compound interest means you earn interest not just on your original deposit (the principal), but also on the interest you've already earned. This creates exponential growth over time. Albert Einstein reportedly called it 'the eighth wonder of the world' — the longer you invest, the more dramatic the effect.
What is the difference between monthly and annual compounding?
With monthly compounding, interest is calculated and added to your balance every month, so you earn interest on interest 12 times per year. With annual compounding, this happens once per year. Monthly compounding results in a slightly higher effective annual rate — for example, a 5% annual rate compounded monthly has an effective annual rate of 5.116%.
How does DIRT affect my savings interest in Ireland?
In Ireland, interest earned in deposit accounts is subject to DIRT (Deposit Interest Retention Tax) at 33%. This is deducted at source by your bank before interest is credited to your account. Our compound interest calculator shows the gross return — use our DIRT Calculator to see the after-tax figure.
What is a good interest rate for savings in Ireland?
As of 2026, Irish banks offer savings rates of approximately 1%–4% depending on the account type and term. State Savings products (from An Post/NTMA) offer competitive tax-free returns for Irish residents. Online and European banks may offer higher rates.
How much will €10,000 grow to in 10 years?
At a 5% annual interest rate compounded monthly, €10,000 grows to approximately €16,470 over 10 years — an increase of €6,470. At 3%, it would reach €13,494. The key variable is time: the same €10,000 invested for 20 years at 5% would grow to approximately €27,126.
Last updated: January 2026 · Rates sourced from Revenue