Future Value of Annuity Calculator

Each contribution earns interest from the moment it is invested until the horizon ends, so the first deposit compounds for the full journey and the last deposit barely compounds at all. The future value sums that geometric series in closed form: payment times one plus r raised to the power of n, minus one, all divided by r, where r is the periodic rate and n is the number of payments. If the return is zero the formula collapses to something trivial — deposits times count — and the ending balance equals exactly what you put in. When contributions are monthly, the annual return is split into twelve monthly rates and the number of payments is years times twelve, so twelve smaller deposits per year slightly outpace one annual deposit at the same nominal rate because each dollar starts compounding sooner. The multiplier — future value divided by total contributions — is the headline intuition number: a figure of 3.5× means every dollar you invested turned into three dollars and fifty cents by the end. The difference between the balance and the deposits is pure compounded growth. Two levers move that growth share almost entirely: the number of periods, which controls how many doubling cycles the early deposits enjoy, and the rate, which controls how fast each cycle runs. Extend either and the growth portion of the balance balloons relative to what you contributed.

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  Back-Solve Your Contribution From a Target

  If you know the nest egg you need — say $1,000,000 at retirement — run the calculator with a realistic return and horizon, then adjust the contribution until the future value meets the target. That reverse-engineered deposit number is the actionable output: it converts a distant goal into a payroll deduction you can set up this week, and it shows how much the target drops if you start five years earlier instead of raising the amount.

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  Automate Before You Optimize

  The formula assumes every contribution actually happens — skipped months are pure lost compounding that no later catch-up fully repairs. Set the contribution as an automatic transfer on payday so the annuity is a fact, not an intention. Then worry about the rate, the account type, and the fund choice; the habit is what keeps the series unbroken.

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  Adjust the Rate for Fees and Inflation

  A quoted 9% average return is not what lands in your pocket. Subtract fund expense ratios, trading costs, and roughly one to two points for taxes if the account is taxable, or simply run the projection at a real (after-inflation) rate of 5–6% to see purchasing-power progress instead of nominal dollars. The calculator is only as honest as the rate you feed it, and conservative inputs produce plans that survive contact with reality.