Savings Calculator: Ending Balance & Interest

How to use this savings calculator

Enter the starting amount, the monthly deposit, the annual rate and the number of years.
Pick how often the interest compounds: annually, quarterly, monthly or daily.
Read the large figure: the ending balance, with the total you contributed and the interest earned alongside.

What a savings calculator is

A savings calculator combines a single starting amount with regular monthly deposits and compounds both at the rate and frequency you choose. The result is the balance at the end of the term, together with how much of that balance came from your own contributions and how much came from interest.

In the default case a $5,000 starting amount plus $200 deposited every month at 5% for 10 years, compounded monthly, reaches an ending balance of $39,291.50. Of that total, $29,000.00 was contributed and $10,291.50 was earned as interest. The starting amount alone would have grown to $8,235.05; the deposits alone would have grown to $31,056.46.

Reading the growth chart

The chart under the result draws your balance across the whole term. The blue line is the ending balance as it builds; it curves upward because interest is added to a growing balance. The orange line is the total you have put in by that point — the starting amount plus every deposit so far — rising in a straight line. The gap between the two lines is the interest earned up to that point, and the dashed line marks the starting amount. Move your mouse over the chart, or touch it, to read the balance, the total contributed and the interest at any month.

The formulas

Ending balance

A = P × (1 + r ÷ n)^{n × t} + PMT × [((1 + i)^{12 × t} − 1) ÷ i], i = (1 + r ÷ n)^{n ÷ 12} − 1

P is the starting amount, PMT the monthly deposit, r the annual rate as a decimal, n the compounding periods per year and t the number of years. Deposits are made at the end of each month, so the deposits part uses i, the monthly rate equivalent to your compounding choice; when interest compounds monthly, i is simply r ÷ 12. On the default figures the starting amount grows to $8,235.05 and the deposits grow to $31,056.46. The two parts are rounded separately for display, so together they can differ from the ending balance by a cent.

Interest earned

Interest earned = ending balance − (starting amount + all deposits)

The ending balance minus everything you put in: the part of the final balance the calculation added rather than you contributed. On the default figures, $39,291.50 − $29,000.00 = $10,291.50.

Total contributed

Total contributed = starting amount + (monthly deposit × number of months)

The starting amount plus every deposit made during the term, with no interest counted. On the default figures, $5,000 + ($200 × 120) = $29,000.00.

Examples

Example	Starting amount	Monthly deposit	Rate	Years	Ending balance	Interest earned
Default	$5,000	$200	5%	10	$39,291.50	$10,291.50
Example 2	$1,000	$100	4%	5	$7,850.89	$850.89
Example 3	$10,000	$500	6%	20	$264,122.49	$134,122.49

All three examples compound monthly.

Three mistakes people make with a savings plan

Entering the rate as a decimal

The rate field takes a percentage. Type 5 for 5%, not 0.05 — entering the decimal shrinks the result to almost nothing.

Reading the ending balance as all earnings

The ending balance includes everything you contributed. In the default case, $29,000.00 of the $39,291.50 is your own money and $10,291.50 is interest earned.

Assuming deposits land at the start of the month

This calculator adds each deposit at the end of the month, so a deposit earns interest from the following month onward. Start-of-month deposits would end slightly higher.

Frequently asked questions

How is the ending balance calculated?

It is the sum of two parts. The starting amount grows with A = P × (1 + r ÷ n)^(n × t), and the monthly deposits grow with the deposits formula. In the default case, the starting amount grows to $8,235.05 and the deposits to $31,056.46, giving an ending balance of $39,291.50.

What is the difference between total contributed and interest earned?

Total contributed is the money you put in: the starting amount plus all deposits. Interest earned is everything above that. In the default case, total contributed is $29,000.00 and interest earned is $10,291.50.

Does the compounding frequency matter?

Yes. You can choose annually, quarterly, monthly or daily, and the formula uses your choice for n. The monthly deposits are converted to the equivalent monthly rate, so they stay monthly whichever frequency you pick. Match the pill to how your account adds interest.

When are the deposits assumed to be made?

At the end of each month. The deposits formula is built on that assumption.

Why does the page show the starting amount as a separate result?

It lets you see how much of the balance comes from the lump sum and how much from the deposits. In the default case, the starting amount alone grows to $8,235.05.

Does the result include taxes, fees or changing rates?

No. The calculator assumes one fixed rate for the whole term and ignores taxes and fees. It runs in your browser and is a calculation aid, not financial advice.

Privacy and important information

This calculator runs entirely in your browser: your numbers are never sent to a server, stored, or shared. It is a calculation aid, not financial advice — real accounts vary with fees, taxes and changing rates.

Part of RahaKit's free finance calculators.

Savings Calculator