How to Calculate What Your Annuity Will Be Worth

The basic formula for future value of an annuity

To calculate the future value of an annuity, you multiply your regular payment amount by a growth factor that accounts for how many payments you'll make and what interest rate they'll earn. The formula is:

FV = PMT × [((1 + r)^n - 1) / r]

In this formula, FV is the future value (the total amount you'll have), PMT is the amount of each payment, r is the interest rate per period (usually expressed as a decimal), and n is the total number of payments. The part in brackets — [((1 + r)^n - 1) / r] — is called the future value factor, and it's what makes the math work. You don't need to memorize this; most people use a calculator, spreadsheet, or annuity table to find it.

Key Takeaways

• The future value formula multiplies your payment amount by a factor that grows with each period's interest and the number of payments you make.
• You need three pieces of information: the payment amount, the interest rate per period, and the total number of payments.
• An ordinary annuity (payments at the end of each period) and an annuity due (payments at the beginning) use slightly different calculations.
• A spreadsheet or financial calculator will do the math for you once you enter the payment, rate, and number of periods.
• The longer your annuity runs and the higher the interest rate, the larger your future value will be.

What information you need to gather first

Before you calculate, write down three numbers. First, the payment amount — how much money goes into the annuity each period (month, quarter, or year). Second, the interest rate per period. If your annuity earns 6% annually but you make monthly payments, you divide 6% by 12 to get 0.5% per month. Third, the total number of payments. If you contribute monthly for 10 years, that's 120 payments.

The interest rate must match the payment period. If you pay monthly, use the monthly rate. If you pay annually, use the annual rate. This is the most common mistake people make — using the wrong rate for the time frame.

You also need to know whether your annuity is ordinary (payments made at the end of each period) or annuity due (payments made at the beginning). Most workplace retirement contributions and savings plans are ordinary annuities. This matters because money paid at the beginning of a period has one extra period to grow.

Using a spreadsheet to calculate future value

The easiest method for most people is a spreadsheet. In Excel, Google Sheets, or similar programs, use the FV function. The syntax is: =FV(rate, nper, pmt). The rate is your interest rate per period as a decimal (0.06 for 6%), nper is the number of periods, and pmt is the payment amount (entered as a negative number, because it's money going out).

For example, if you contribute $500 monthly to an annuity earning 6% annually for 10 years, you would enter: =FV(0.06/12, 120, -500). The spreadsheet returns approximately $77,640. That's your future value — the total amount in the annuity after 10 years of $500 monthly contributions earning 6% per year.

If your annuity is annuity due (payments at the beginning of each period), add a fourth parameter: =FV(rate, nper, pmt, 1). The 1 tells the spreadsheet to calculate for annuity due instead of ordinary annuity. The result will be slightly higher because each payment has one extra period to earn interest.

Working through a step-by-step example

Let's say you want to know the future value of an annuity where you deposit $300 every quarter for 5 years, and the annuity earns 4% annually. Here's how to set it up:

First, convert the annual rate to a quarterly rate: 4% ÷ 4 = 1% per quarter, or 0.01 as a decimal. Next, count the total payments: 5 years × 4 quarters = 20 payments. Now plug into the formula: FV = $300 × [((1 + 0.01)^20 - 1) / 0.01]. The future value factor works out to about 22.019, so FV = $300 × 22.019 = $6,605.70.

This means after 5 years of $300 quarterly deposits earning 4% annually, you'll have approximately $6,605.70. Of that, $6,000 came from your own contributions ($300 × 20 payments), and about $605.70 came from interest earned.

How interest rate and time affect your result

The longer your annuity runs, the more your money grows. This is because each payment earns interest for a different length of time. Your first payment earns interest for the full period; your last payment earns little or no interest. The more payments you make, the more total interest compounds.

A higher interest rate also increases your future value significantly. If the same $300 quarterly annuity earned 6% instead of 4%, your future value after 5 years would be about $7,100 instead of $6,605 — an extra $500 from the higher rate alone. Over longer periods, this difference grows much larger.

This is why even small differences in interest rates matter for long-term annuities. A 1% difference might seem small, but over 20 or 30 years, it can add thousands of dollars to your final amount.

Ordinary annuity versus annuity due

An ordinary annuity assumes payments happen at the end of each period. An annuity due assumes payments happen at the beginning. This timing difference means annuity due payments have one extra period to earn interest, so the future value is always higher.

Using the same $300 quarterly example at 4% for 5 years: ordinary annuity gives $6,605.70, but annuity due gives about $6,670. The difference is small in this case but grows larger with higher rates or longer periods. Most employer retirement plans and regular savings accounts work as ordinary annuities, so that's the calculation you'll use most often.

When to use annuity tables instead of formulas

Before calculators and spreadsheets, people used printed annuity tables that listed pre-calculated future value factors. You can still find these tables online or in finance textbooks. They're organized by interest rate and number of periods, and you straightforward find the factor that matches your situation, then multiply it by your payment amount.

Annuity tables are useful if you don't have access to a calculator or spreadsheet, or if you want to double-check a calculation. However, they only work for standard rates and periods — if your rate or number of periods falls between the table values, you'll need to estimate or use a formula instead. For most people today, a spreadsheet or financial calculator is faster and more accurate.

Frequently Asked Questions

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

Future value tells you how much money you'll have at the end of making all your payments. Present value tells you what all those future payments are worth in today's dollars. If you're saving money, you care about future value. If you're receiving payments from an annuity, you might care about present value to understand what you're getting.

Do I need to adjust the interest rate if I make payments more often than once a year?

Yes. If you make monthly payments but the annuity earns an annual rate, divide the annual rate by 12 to get the monthly rate. If you make quarterly payments, divide by 4. The rate must always match the payment frequency, or your calculation will be wrong.

What if the interest rate changes during the annuity period?

The basic formula assumes a constant rate. If your rate changes, you'll need to break the calculation into separate periods — calculate the future value up to the rate change, then use that amount as the starting point for the next period with the new rate. Your annuity provider can tell you how rate changes are handled in your specific contract.

Can I calculate future value if I make irregular payments?

The standard annuity formula assumes equal payments at regular intervals. If your payments vary in amount or timing, you'll need to calculate the future value of each payment separately and add them together, or use specialized financial software designed for irregular cash flows.

Why does my calculation differ slightly from what my provider shows?

Small differences usually come from rounding, the exact day payments are processed, or how interest is compounded (daily, monthly, or annually). Ask your provider for their specific calculation method. Large differences might mean you're using the wrong rate, the wrong number of periods, or the wrong annuity type (ordinary versus due).