A teacher retires at 65 with $400,000 saved and one burning question: how big a monthly check can that pile write, and for how long? A retirement annuity answers by converting a lump sum into a guaranteed stream of payments. Insurance companies and pension funds price these streams with the same present-value math you use for a mortgage, only reversed — instead of borrowing a lump sum and repaying it, you hand over the lump sum and collect it back, with interest, one check at a time.

This calculator runs the numbers both ways. Enter your starting balance as the present value — try $400,000 — the annual rate the annuity credits, say 5 percent, and the payout length, say 240 months for a 20-year certain annuity. The tool returns the monthly payment, roughly $2,638, plus the total paid out and how much of it is interest versus your own principal. Flip to accumulation mode to see what monthly contributions grow into: $500 a month at 6 percent for 30 years compounds to about $502,000. Social Security keeps coming regardless, but this math shows exactly what your savings add on top.

Treat the result as a planning baseline, not a contract quote. Real annuity payouts subtract fees, mortality credits, and the insurer's margin, and inflation quietly shrinks every fixed check — $2,638 buys far less in year 20 than in year 1. Use the numbers to compare lump-sum-versus-income choices, then get actual quotes before signing anything.

With the pre-filled defaults — Present Value (Initial) $100,000, Regular Payment Amount $1,000, Annual Interest Rate 5%, Number of Periods (Months) 120, Annuity Type Ordinary (End of Period) — the Retirement Annuity Calculator returns Future Value $155,282.28, Total Payments Made $120,000.00, Total Interest Earned $35,282.28, Present Value of Annuity $94,281.35. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.