🏦 Compound Savings Calculator
See how your savings grow with compound interest and regular deposits.
Results
Growth by year
| Year | Deposits | Interest | Balance |
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An estimate only. It assumes a fixed rate and no tax, fees or inflation. A deposit made part-way through a period earns a share of that period's interest. Real accounts may work out interest differently.
Why use this calculator?
Compound interest is the one piece of arithmetic that decides what saving does, and it is invisible on a single bank statement: the interest paid next year depends on the interest already added. This calculator grows a balance at a fixed rate with money going in regularly, so you can see what a term deposit, a savings account or a house deposit plan actually comes to. It also answers the question a savings account never spells out: how much of the final figure is money you put in, and how much of it the bank did.
How does this calculator work?
Interest is worked out at the rate that matches the compounding you chose, and added to the balance each time it comes round:
interest for one period = balance × (rate ÷ 100 ÷ periods per year)
so 5% compounded monthly is 5% ÷ 12 each month, worked out on a balance that has already grown by every earlier lot. Over a whole term that is the familiar equation, where the money goes in and nothing comes out:
A = P × (1 + r ÷ m)^(m × t)
with P the starting balance, r the yearly rate, m how many times a year interest is added and t the term in years. Regular deposits turn it into a sum rather than one figure, so the term is stepped through in units that suit both frequencies at once — a daily rate with weekly deposits is counted in 1/18,980ths of a year, so nothing drifts out of line:
- Interest builds up on the balance as time passes and is added at each compounding point, which is why a "per annum" rate still moves the balance the moment the period turns over.
- A deposit made part-way through a period earns a share of that period's interest, and a deposit at the start of a period earns a little more than the same deposit at the end of it, because it is there for longer.
- The final balance includes interest that has built up but has not been added yet, so a term ending mid-way through a compounding period is not short-changed.
- The effective yearly rate is (1 + rate ÷ 100 ÷ m)^m − 1: the rate with compounding folded in, which is the figure to compare one account with another.
Frequently asked questions
Which compounding option matches my account?
Most savings accounts add interest once a month, so monthly is the safe answer; some advertise daily interest, in which case choose daily. The gap between the two is small — on 5%, daily compounding comes to about 5.13% a year against 5.12% for monthly — but it is real, and the effective yearly rate in the results is the quickest way to see your own version of it.
Should deposits go in at the start or the end of a period?
Whichever your account does. Money that arrives before the interest is worked out behaves like the start of the period and earns interest straight away; money that arrives after it behaves like the end. If you are not sure, the end of the period is the conservative choice, because it gives every deposit the least possible time to earn.
What is the effective yearly rate for?
It folds compounding into one figure: the rate your balance would have to grow at, once a year, to end up in the same place. That is what makes two accounts comparable when one compounds daily and the other monthly, or when a bonus rate applies for the first few months only.
Does it include tax on the interest, or inflation?
No. Interest is taxed at your marginal rate in the year it is earned, so the balance here is bigger than what you keep, and a dollar in 20 years buys less than a dollar today. For a long term, the honest comparison is a lower rate rather than a higher one.
Can I use it for a lump sum with no deposits?
Yes. Leave the deposit at 0 and put the whole amount in the starting balance. The calculator needs one of the two, so it will say so if both are empty, and the results then show the interest earned on the lump sum alone.
What about fees, bonus rates or a rate that changes?
None of them are here. The rate is fixed for the whole term, which is what makes one run possible: a bonus rate that drops after six months, or an introductory rate on a new account, needs a separate run for each period. Account fees come straight off the balance, so subtract them from the rate if you want a rough answer.