How to Calculate What Your Annuity Will Be Worth

The formula for future value of an annuity

The future value of an annuity tells you how much money you will have accumulated after making regular payments into an investment over time, assuming a fixed interest rate. The calculation depends on whether you make payments at the beginning or end of each period — this matters because money paid in earlier earns more interest.

For an ordinary annuity (payments at the end of each period), the formula is:

FV = PMT × [((1 + r)^n − 1) / r]

For an annuity due (payments at the beginning of each period), multiply the ordinary annuity result by (1 + r).

In both formulas: PMT is your payment amount per period, r is the interest rate per period, and n is the total number of periods. The caret symbol (^) means you raise the number to a power — so (1 + r)^n means multiply (1 + r) by itself n times.

Key Takeaways

• Future value of an annuity shows how much your regular payments will grow to, given a fixed interest rate and time period.
• Ordinary annuities have payments at the end of each period; annuities due have payments at the beginning, which produces a higher total.
• You need four numbers to calculate: your payment amount, the interest rate per period, the number of periods, and whether payments are at the start or end of each period.
• A spreadsheet or financial calculator will compute this faster than doing it by hand, but understanding the formula helps you spot errors in results.

Breaking down each part of the formula

The formula has three main pieces. PMT is straightforward — it is the dollar amount you deposit or invest each period. If you contribute $500 per month, PMT = 500.

r is the interest rate per period, written as a decimal. If your annual rate is 6%, and you make monthly payments, you divide 6% by 12 months to get 0.5% per month, or 0.005 as a decimal. This is critical: the rate must match the period. If you pay monthly, use the monthly rate. If you pay annually, use the annual rate.

The part ((1 + r)^n − 1) / r is called the future value factor. It captures how much your money grows through compounding. The exponent n is the total number of periods — if you make monthly payments for 10 years, n = 120 (12 months × 10 years). The factor grows larger as n increases, which is why longer time horizons produce bigger totals.

A worked example with monthly payments

Suppose you invest $300 per month into an account earning 4.8% annual interest, compounded monthly, for 5 years. Here is how to calculate the future value.

First, convert the annual rate to a monthly rate: 4.8% ÷ 12 = 0.4% per month = 0.004 as a decimal. Next, count the periods: 5 years × 12 months = 60 periods. Assume payments happen at the end of each month (ordinary annuity).

Now plug into the formula: FV = 300 × [((1.004)^60 − 1) / 0.004]. Calculate (1.004)^60, which equals approximately 1.2705. Subtract 1 to get 0.2705. Divide by 0.004 to get 67.625. Multiply by 300 to get $20,287.50. After 5 years of $300 monthly payments, your account will hold roughly $20,288.

If instead you made payments at the beginning of each month (annuity due), multiply that result by (1 + 0.004) = 1.004. The future value becomes $20,287.50 × 1.004 = $20,375.15 — about $87 more because each payment had one extra month to earn interest.

Using a spreadsheet or calculator instead of doing it by hand

Most people use a tool rather than calculate by hand. In Excel or Google Sheets, the function is FV(rate, nper, pmt, [pv], [type]). The rate is the interest rate per period, nper is the number of periods, pmt is the payment amount (entered as a negative number), pv is the present value (usually 0 if you are starting from scratch), and type is 0 for ordinary annuity or 1 for annuity due.

For the example above, you would enter: =FV(0.004, 60, -300, 0, 0). The result is $20,287.50, matching the hand calculation. A financial calculator with an FV button works the same way — enter the rate, number of periods, and payment, then press FV to see the result.

Using a tool is faster and reduces arithmetic errors, especially when the numbers are large or the time period is long. However, you still need to know what numbers to enter, which is why understanding the formula matters.

Why the timing of payments changes the result

An ordinary annuity and an annuity due produce different totals because of when money enters the account. In an ordinary annuity, your first $300 payment sits in the account for 59 months (not 60) before the calculation ends. In an annuity due, it sits for 60 months. That extra month of compounding adds up across all your payments.

The difference grows larger as the interest rate rises or the time period lengthens. At 2% annual interest over 5 years, the gap is small. At 8% annual interest over 20 years, an annuity due can be 8% to 10% higher than an ordinary annuity. Always confirm with your bank or investment provider whether your payments are made at the start or end of the period — it affects the final number.

Common mistakes when setting up the calculation

The most frequent error is mismatching the interest rate and the period. If you have an annual rate of 5% but make quarterly payments, you must divide 5% by 4 to get 1.25% per quarter. Forgetting this step will give you a wildly incorrect result.

Another mistake is counting periods wrong. If you contribute monthly for 3 years, the count is 36 periods, not 3. Spreadsheet functions expect the number of periods, not the number of years.

A third error is entering the payment as a positive number when the formula or function expects a negative number. In most spreadsheet functions, money going out (your payment) is negative, and the result (money coming in) is positive. Check your tool's documentation to see which sign convention it uses.

How inflation and taxes affect real future value

The formula gives you a nominal future value — the dollar amount in the account, without accounting for inflation or taxes. If inflation averages 2.5% per year and your annuity earns 4.8%, your real purchasing power grows at roughly 2.3% per year. After 5 years, your $20,288 will buy less than it would today.

Taxes also reduce what you keep. If the interest earned is taxable, you owe tax on the gains, not just the principal. In the example above, you contributed $18,000 (300 × 60 months) and earned $2,288 in interest. Depending on your tax bracket and whether the account is tax-deferred, you may owe tax on some or all of that $2,288. The future value formula does not account for this — you have to subtract taxes separately.

Frequently Asked Questions

What is the difference between future value and present value of an annuity?

Future value tells you what your regular payments will grow to at a future date. Present value tells you what a stream of future payments is worth in today's dollars. If you want to know how much you will have saved, use future value. If you want to know what a pension or payout is worth right now, use present value.

Do I use the annual interest rate or the monthly rate in the formula?

Use the rate that matches your payment period. If you pay monthly, convert the annual rate to a monthly rate by dividing by 12. If you pay quarterly, divide by 4. The rate and the period must align, or the calculation is wrong.

Why is my spreadsheet result different from my calculator result?

Check whether you entered the payment as positive or negative — different tools use different sign conventions. Also verify that you set the type correctly (0 for ordinary annuity, 1 for annuity due). A small difference in rounding is normal, but a large gap usually means one of these settings is wrong.

Can I use this formula if my interest rate changes each year?

No, this formula assumes a constant rate. If your rate changes, you have to break the calculation into segments — calculate the future value for the first period at the first rate, then use that result as the starting point for the next period at the new rate. A spreadsheet makes this easier than doing it by hand.

Does the future value formula work for loans or only for savings?

The formula works for any regular payment stream with a fixed interest rate. For a loan, you would use it to calculate how much you will have paid in total, including interest. For savings or investments, it shows how much you will have accumulated. The math is the same; the context changes what the number means.