Compound-savings guide: monthly growth and deposits

When this tool helps

Compound savings combines growth on the starting amount with growth on later contributions. The timing of those contributions matters: this candidate assumes each monthly deposit is added at month-end. It is a scenario calculation, not a forecast of market returns.

Enter starting savings, a monthly contribution, the annual percentage rate and a whole number of months. A currency label helps keep the money inputs consistent but does not fetch exchange rates. Compare scenarios rather than treating a single assumed rate as certain.

What to enter

These are the candidate Android fields, not a form on this website. Editable fields in the app start empty; modes and units are selected separately.

Starting savings: The amount present before the first month.
Monthly contribution: The same amount added at each month-end.
Annual interest rate (%): Your constant-rate assumption.
Number of months: Whole months from 1 to 1,200.

Worked example · not prefilled app data

Try this example after the update is available

The values below explain the calculation. They are not a quote, a live measurement or an automatic answer for your situation.

Starting savings: 1000
Monthly contribution: 100
Annual rate (%): 5
Number of months: 12

Checked example result2,279.05

Starting with 1,000.00 and adding 100.00 at each of twelve month-ends contributes 2,200.00. At the entered constant 5% annual rate with monthly compounding, the displayed scenario total is 2,279.05.

Formula and assumptions

Future value = P(1+r)^n + D[(1+r)^n − 1] ÷ r; monthly r = annual percentage ÷ 1,200

At zero interest, total is starting savings plus monthly contribution multiplied by months.
Rates are non-negative and constant; fees, taxes, inflation, variable returns and withdrawals are excluded. Returns are not guaranteed.

A common mistake to avoid

Do not confuse a nominal annual rate divided monthly with an annual effective return or a variable investment return. Different conventions produce different totals.

Find this tool in the Android update

When you have the redesigned Android update, open Tools and search for Compound savings, or find it under Money.
Open the tool, choose the mode or units relevant to your task, then enter your own values.
Review the result and explanation. Use Calculate & save only if you want the calculation kept in local History; Copy result does not send it to our server.

This guide is an educational preview of the update in testing, not an announcement that Google Play has approved or published it. Calculations are in the native app; no web calculator or download is offered on this page.

Questions about Compound savings

Are deposits made at the beginning of the month?

No. This candidate assumes deposits at month-end, so the last deposit has no remaining month of growth.

Is the calculated interest guaranteed?

No. The result follows the rate you enter; it is not a product offer, prediction or investment recommendation.