Savings Growth Calculator

When to use it

Regular saving is a slow, boring, extremely effective habit, and this page makes the slowness visible: a starting balance, a monthly deposit and a return, projected year by year. It answers questions like how much a deposit fund will hold in five years, or what a small monthly transfer is really worth over a decade.

The figures are nominal: before tax, before fees, and before inflation. Treat the rate as a scenario, not a promise, and run a low and a high version to see the range you should plan around.

How the maths works

Balance = start × (1 + r)^n + deposit × ((1 + r)^n − 1) ÷ r. Here r is the annual return divided by 1,200 and n is the number of months. The first term grows the opening balance; the second is the future value of an ordinary annuity, because each deposit is made at the end of its month and therefore earns one month less interest than the balance before it.

With a zero return the second term collapses to deposit × n, which is exactly what you paid in. The detail line always shows the total contributed and the interest as separate numbers.

A worked example

1,000 to start, 200 a month, 4% a year, for five years.

1. Monthly rate: 4 ÷ 1,200 = 0.003333, and n = 60 months.
2. Growth factor: 1.003333^60 = 1.2210.
3. Opening balance grows to 1,000 × 1.2210 = 1,220.99.
4. Deposits: 200 × ((1.2210 − 1) ÷ 0.003333) = 13,259.80, for a total of 14,480.79.

You paid in 13,000 and earned 1,480.79. Five years is short: most of the growth still comes from the deposits, not from the return.

Year by year

The interest column grows faster than the balance: in year one it is 85, in year five the year alone adds over 500. That acceleration is the whole argument for starting early.

Common mistakes

• Assuming deposits are made at the start of the month. They are not, so a start-of-month saver would earn slightly more than shown.
• Treating the return as fixed. Markets fall; the projection is a straight line and reality is not.
• Ignoring tax and fees. Both come off the interest, and a small annual fee compounds against you.
• Changing the deposit halfway. The page holds it constant; for a rising deposit, run separate periods and add the results.

Keep exploring

• Compound Interest Calculator — the same growth with a lump sum only.
• Savings Goal Calculator — the monthly amount needed to hit a target.
• CAGR Calculator — the yearly rate your final balance implies.
• Guide: Understanding Compound Interest.