Rex says
Money math without the spreadsheet headache. Plug in your numbers and I'll show you exactly where the dollars land.
Try a scenario
Click to load — tweak from there.Inputs
Result
Monthly payout
$2,639.82
Annual income
$31,678
Total paid out
$633,558
Interest earned
$233,558
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter lump sum ($).
- 2Enter annual rate (%).
- 3Enter payout period (years).
- 4Read your monthly payout on the right — it updates as you type.
- 5Hit Share to keep the scenario or send it to someone.
About this calculator
An immediate annuity converts a lump sum into a guaranteed income stream. This calculates the monthly payout a given premium supports over a fixed period at a stated rate.
Worked example
Using the values the calculator loads with:
Inputs
- Lump sum: 400000 $
- Annual rate: 5 %
- Payout period: 20 years
Results
- Monthly payout: $2,639.82
- Annual income: $31,677.88
- Total paid out: $633,557.51
- Interest earned: $233,557.51
What each field means
Inputs
- Lump sum ($)
- The lump sum used in the calculation, measured in $. Starts at 400000 $ so you have a working example on load.
- Annual rate (%)
- The annual rate used in the calculation, measured in %. Starts at 5 % so you have a working example on load.
- Payout period (years)
- The payout period used in the calculation, measured in years. Starts at 20 years so you have a working example on load.
Results
- Monthly payout
- Returned as a money amount in US dollars and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Annual income
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Total paid out
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Interest earned
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the annuity calculator work?
An immediate annuity converts a lump sum into a guaranteed income stream. This calculates the monthly payout a given premium supports over a fixed period at a stated rate. The underlying maths is: Payment = Principal × r ÷ (1 − (1 + r)^−n), where r is the monthly rate.
What do I need to enter?
3 values: lump sum, annual rate, and payout period. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the monthly payout result mean?
It is returned as a money amount in US dollars and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
Who is this tool for?
It's built for anyone comparing money scenarios before committing — budgeting a payment, sanity-checking a quote, or seeing what a change in rate or term actually costs.
Accuracy and limitations
- Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
- Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.
- This is educational maths, not financial advice. Check anything contractual with the lender or your accountant.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Annuity Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/annuity
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/annuity" target="_blank" rel="noopener">Annuity Calculator — RevenueLab</a> (2026).</p>
Source: [Annuity Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/annuity) (2026).