Compound Interest Calculator

When this calculator is useful

Compounding rewards patience, and the earlier you begin the more it does the heavy lifting. Use this calculator when you are planning across euro-denominated savings and investments — a regular savings account, an ETF savings plan, a life-insurance or pension product, or a private pillar arrangement — and you want a realistic sense of where a pot might land over the years. It is for orientation, not for promising an exact outcome.

It suits the practical questions savers across the euro area ask: what could a €100-a-month ETF plan be worth in two decades, does paying in earlier really matter that much, how much difference does one extra percentage point of return make. You set an opening amount, a monthly contribution and an expected rate, and it builds the balance period by period.

Understanding your result

The final figure is made of two parts: your total contributions (opening amount plus every monthly payment) and the compound growth added on top. The growth portion is the one to watch — it is small at first and then accelerates, because returns begin earning returns of their own. Over long horizons that compounding is where most of the balance comes from.

Read it as a pre-tax estimate based on a constant assumed return. Real markets do not move in a straight line, so no single year will match the average. A 5% assumption is a cautious long-run middle for a diversified equity ETF portfolio across a full cycle; euro-area savings accounts have often paid very little, so use a much lower rate for pure cash.

A worked example

Open an ETF savings plan with €1,000, add €100 a month, and assume 5% a year for 20 years. You pay in €25,000 of your own money, and compounding could add roughly €16,000 on top — a balance of around €41,000. Raise the assumption to 7% and the growth roughly doubles, which shows how much the outcome hinges on the rate you choose and the fees you pay.

Points to be careful about

Across the euro area the usual pitfalls are optimistic return assumptions and overlooking fees, tax and inflation.

• Entering a gross return without deducting fund and platform fees — even a 1% annual charge erodes the pot heavily over decades.
• Forgetting inflation — €41,000 in 20 years will buy noticeably less than €41,000 buys today.
• Assuming the rate is fixed; the value of investments can fall as well as rise.
• Treating one country's tax treatment as universal — it is not across the euro area.

Euro-area tax and product notes

Tax on savings and investments is not harmonised across the euro area, so the treatment of interest, dividends and capital gains differs sharply from one member state to the next — flat withholding taxes in some countries, progressive rates or wealth taxes in others, and a range of tax-advantaged pension wrappers. Some countries also tax unrealised gains on certain products.

Because of that variation, this calculator deliberately shows pre-tax figures only and applies no country-specific rules. For how the result would be taxed where you live, check your national tax authority or speak to a qualified local adviser before making decisions.