Compound interest calculator
How far can capital grow with a contribution every month? Enter the starting capital, the contribution, an assumed return and the years: the calculator shows what you paid in, what comes from interest and what the total is worth in today's money.
Final capital
€ 109,333
In today's euros
€ 73,578
Net of inflation
Total paid in
€ 58,000
Interest earned
€ 51,333
Contributions and interest over time
Estimates for information only, not financial or tax advice: the results depend on the assumptions entered, and past returns do not guarantee future ones.
How compound interest works
With compound interest each period's interest is added to the capital and earns interest in turn. That is why growth is not a straight line: in the early years what you pay in weighs most, in the later ones the interest does.
The calculator applies the annual return divided by the number of contributions per year: with monthly contributions and a 5% return, each month the capital grows by 0.4167% and then receives the contribution.
Nominal and real
The nominal final capital is the figure you will see in the account. The real one is the same figure in today's euros, discounted by the assumed inflation: it is the number that tells you what you will really be able to buy.
The limits of a simulation
- The return is the same every year: in reality markets rise and fall, and the order of returns changes the result when you invest over time.
- Product costs, fees, stamp duty and taxes on gains are left out, and they lower the result.
- The calculator does not suggest a return: try several assumptions, prudent ones included, and see how the result changes.
Frequently asked questions
Which return should I enter?
The calculator does not give an expected return. Try several assumptions and compare the results: a market's past returns do not guarantee future ones.
What counts more, the starting capital or the monthly contribution?
It depends on the amounts and the years. The year-by-year table shows the total paid in and the interest earned separately, so you can compare scenarios.
Are taxes included?
No. In Italy gains on ETFs and shares are taxed at 26% when you sell or receive them, on government bonds at 12.5%, and a 0.2% stamp duty is due each year on the value.
From the simulation to your savings plan
In PortFolk you set up your savings plans, get each instalment proposed split across the instruments, and see the projection toward the portfolio's target value, on the trades you actually make.
The demo is a sample portfolio, already filled in: it opens without signing up. The Free plan asks for no card.
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