Benjamin Franklin’s will (1790) left £1,000 each to Boston and Philadelphia on 200-year compound-interest terms — the Boston fund reached $5 million in 1990.
§01What is
Understanding the Future Value of Annuity
The Future Value of Annuity computes FV of annuity from 3 inputs: payment ($), rate (%), periods. FV of an annuity.
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The Future Value of Annuity sits in that toolkit — it FV of an annuity. Enter your numbers above and the result updates instantly; every step of the math is shown in the Derivation panel so you can see exactly how the answer was reached.
§02The Formula
How it’s calculated
t × (((1+a / 100 / 12)^(n)-1) / (a / 100 / 12))
Where
PMT
Payment ($)
r
Rate (%)
n
Periods
§03Practical Example
Step-by-step walkthrough
Scenario
Apply the formula to a realistic set of inputs: Payment ($) = 200, Rate (%) = 5, Periods = 120.
01Start by noting the input — Payment ($): 200.
02Start by noting the input — Rate (%): 5.
03Start by noting the input — Periods: 120.
04Substitute these values into the formula: t × (((1+a / 100 / 12)^(n)-1) / (a / 100 / 12))
05Compute FV of annuity: the calculator returns 31056.5.
06Cross-check the answer by opening the Derivation panel above — every line of math is shown so you can follow the computation end-to-end.
§04Variants
Common Future Value of Annuity Problems
The formula gets rearranged depending on which variable you need. Here are the patterns you’ll run into in the real world — find the one that matches your problem and follow the worked steps.
01 · PATTERN
Payment ($) halved
PMT = 100 (from 200)
Keep every other input at its default and halve the payment ($). See how fv of annuity responds.
01New Payment ($): 100
02Baseline FV of annuity: 31056.5
03New FV of annuity: 15528.2
04FV of annuity decreases by 50% → use this sensitivity to plan for real-world variation.
02 · PATTERN
Payment ($) doubled
PMT = 400 (from 200)
Keep every other input at its default and double the payment ($). See how fv of annuity responds.
01New Payment ($): 400
02Baseline FV of annuity: 31056.5
03New FV of annuity: 62112.9
04FV of annuity increases by 100% → use this sensitivity to plan for real-world variation.
03 · PATTERN
Rate (%) halved
r = 2.5 (from 5)
Keep every other input at its default and halve the rate (%). See how fv of annuity responds.
01New Rate (%): 2.5
02Baseline FV of annuity: 31056.5
03New FV of annuity: 27234.4
04FV of annuity decreases by 12.3% → use this sensitivity to plan for real-world variation.
04 · PATTERN
Rate (%) doubled
r = 10 (from 5)
Keep every other input at its default and double the rate (%). See how fv of annuity responds.
01New Rate (%): 10
02Baseline FV of annuity: 31056.5
03New FV of annuity: 40969
04FV of annuity increases by 31.9% → use this sensitivity to plan for real-world variation.
§05FAQ
Frequently asked questions
Yes. The calculator implements the standard formula as documented and returns exact floating-point results. No approximations are used unless noted in the formula.
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