Annuity Payment Calculator

What it does

Calculate periodic payments for any annuity — given a principal amount, interest rate, and term, the tool returns monthly, quarterly, or annual payment values. Useful for retirement-income planning (you have $500K saved; how long does it last at $4K/month at 5%?); structured-settlement analysis (offer to pay $50K/year for 20 years vs $750K lump sum — which is better?); loan amortization (the same math works for fixed-rate mortgages, car loans, student loans); perpetuity sanity-checks (how much principal do you need to safely withdraw $X/year forever?).

The annuity formula: PMT = P × [r(1+r)n] / [(1+r)n − 1]where P = principal, r = periodic interest rate (annual rate ÷ frequency), n = total number of payments. For a $300K mortgage at 6% annual over 30 years (360 monthly payments): r = 0.06/12 = 0.005, n = 360, PMT = 300000 × (0.005 × 1.005³⁶⁰) / (1.005³⁶⁰ − 1) ≈ $1,799/month.

Annuity types:

• Ordinary annuity: payments at the END of each period. Most common for loans (you pay interest accrued during the period). The default formula above is for ordinary annuities.
• Annuity due: payments at the START of each period. Used for rent / lease payments. Slightly different math (multiply ordinary annuity payment by (1+r) to get annuity-due payment for the same other parameters).
• Perpetuity: payments continue forever. PMT = P × r (so $1M at 4% → $40K/year forever, in theory). Useful for endowment / trust planning.
• Growing annuity: payments grow at a fixed rate per period (e.g. inflation-adjusted withdrawals). Different formula; the calculator can handle this with the growth-rate input.

For real-world financial planning, the calculator gives a precise mathematical answer — but real retirement plans need to account for variable returns (sequence-of-returns risk), inflation, taxes, medical-expense surprises, and longevity risk (living past 95). A 4% withdrawal rate (Bengen, 1994 / Trinity Study) is the rule of thumb for retirement sustainability; it’s NOT the same as “pick a rate, divide your money, withdraw forever.”

How to use it

1. Enter principal (the lump sum you'll be drawing from, or the loan amount you'll be paying down).
2. Enter interest rate (annual percentage; the tool converts to periodic rate based on payment frequency).
3. Set the term in years.
4. Pick payment frequency: monthly (most common), quarterly, or annual.
5. Optionally pick annuity-due (payments at start of period — for rent/lease) instead of ordinary annuity (end of period — for loans, default).
6. Read the periodic payment. The tool also shows the total amount paid over the life of the annuity (principal + interest).

When to use this tool

• Retirement-income planning — estimate sustainable monthly withdrawals from a nest egg.
• Mortgage / loan calculations — verify the lender's quoted payment is correct given the rate and term.
• Comparing structured-settlement offers — lump sum vs annual payments.
• Estate / trust planning — how much principal generates X annual income at sustainable rate.

When not to use it

• Variable-rate investments — annuity math assumes fixed rate. Real markets have sequence-of-returns risk; use Monte-Carlo simulation tools (cFIREsim, FIRECalc) for realistic retirement planning.
• Tax-advantaged scenario comparisons (Roth IRA vs Traditional vs taxable) — annuity math doesn't capture tax differences. Use a tax-aware retirement calculator.
• Insurance-product annuities (immediate annuity, deferred annuity, variable annuity) — those have insurance overlays (mortality risk pooling, fees, surrender charges) that pure-math doesn't capture. Read the contract.

Common use cases

• Quick calculation during a typical workday
• Pre-decision sanity-check on inputs and outputs
• Educational use — demonstrating the underlying concept
• Onboarding a colleague who needs the same calculation/conversion