Annuity Calculator
Model both phases of an annuity. In the growth phase, compound a starting balance plus monthly or annual deposits to a future value. In the payout phase, solve the level income a fund can pay and how long it lasts. Switch payment timing between end of period (ordinary) and beginning of period (annuity due).
Formula
Worked example
Start with $0 and add $400/month for 20 years at 6% (i = 0.5%/month, n = 240): the deposit stream grows to about $184,800. You contributed $96,000, so roughly $88,800 is interest. In payout, a $250,000 fund at 6% over 20 years pays about $1,791 per month before it is exhausted.
Growing an annuity (the accumulation phase)
The growth phase compounds three things: any starting balance you already hold, a fixed monthly deposit, and an optional once-a-year deposit. Each is grown at the same fixed rate, applied monthly, so the annual rate is divided by 12 to get the periodic rate and the years are multiplied by 12 to get the number of periods. The starting balance grows as P times (1 + i) to the power n. The monthly deposits form an ordinary annuity that grows by the factor ((1 + i)^n minus 1) divided by i. Adding these together gives the future value, and subtracting the money you put in leaves the interest earned.
Turning a fund into income (the payout phase)
The payout phase reverses the question: given a lump sum, what level monthly income drains it to zero over a chosen number of years? This is the present-value annuity formula solved for the payment, PMT = F times i divided by (1 minus (1 + i) to the power minus n). The calculator also reverse-solves the other direction: enter a target monthly income and it shows how many years the fund lasts at that draw. If your target income is below the interest the fund earns each month, the balance never falls, so the income is effectively perpetual.
Ordinary annuity versus annuity due
Payment timing matters. With an ordinary annuity, payments land at the end of each period, the default for most savings and loan math. With an annuity due, payments land at the start of each period, common with rent and some insurance products, and every payment earns one extra period of interest. Switching to annuity due multiplies the accumulation result by (1 + i) and lowers the income a fund can pay for the same horizon, because each withdrawal is taken a period earlier. Use the timing selector to match the product you are modeling.
What the projection does and does not include
These figures are mathematical projections at a single fixed rate with uninterrupted, level payments. They do not model taxes, fees, surrender charges, inflation, or the variable returns of real markets, and they are not a quote from any insurer. Commercial annuity products also bundle in mortality credits, riders and guarantees that change the payout. Treat the output as a planning estimate, then confirm any real annuity purchase with a licensed adviser and the actual contract terms.
Annuity terms used here
| Term | Meaning | In the formula |
|---|---|---|
| Starting balance (P) | Lump sum already in the account | P(1 + i)^n |
| Monthly rate (i) | Annual rate ÷ 12 | i = r / 12 |
| Periods (n) | Years × 12 | n = years × 12 |
| Ordinary annuity | Payment at period end | standard factor |
| Annuity due | Payment at period start | factor × (1 + i) |
| Payout (PMT) | Income that drains the fund | F·i / (1 - (1+i)^-n) |
A quick reference for the inputs and how they enter the math.
Frequently asked questions
What is the difference between the growth and payout modes?
Growth mode compounds a starting balance plus monthly and annual deposits forward to a future value, the accumulation phase. Payout mode does the reverse: it takes a fund and solves the level monthly income that would drain it to zero over your chosen number of years, and it can also tell you how long a target income would last.
Does this calculator compound monthly or annually?
It compounds monthly. The annual rate is divided by 12 to get the periodic rate and the years are multiplied by 12 to get the number of periods, which matches how most annuities and savings accounts actually credit interest. The yearly schedule simply rolls up those monthly steps.
What is the difference between an ordinary annuity and an annuity due?
An ordinary annuity pays at the end of each period; an annuity due pays at the beginning. Because each annuity-due payment compounds one extra period, choosing annuity due raises the accumulated future value (by a factor of 1 + i) and lowers the income a fund can sustain over the same horizon.
Is the projected balance or income guaranteed?
No. The result is a mathematical projection assuming a single fixed rate and uninterrupted, level payments. It excludes taxes, fees, surrender charges, inflation, and the variable returns of real markets, and it is not a quote from any insurer. Treat it as a planning estimate.