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A $650/month quote on $100k is a 4.82% implied rate. Now you can check any offer.
Annuity quotes are sold as a monthly number precisely because a monthly number is hard to grade. This calculator converts both directions: forward — the exact period-certain payout any lump sum produces at a given rate — and reverse — the implied interest rate hiding inside any insurer quote, solved to the hundredth of a percent. Compare that implied rate against safe CD and Treasury yields and the "is this annuity any good?" question answers itself.
Anyone holding an insurer's monthly-income quote uses it to compute what the agent never volunteers: the implied interest rate. A $650/month promise on $100k is a 4.82% rate — and whether that beats Treasuries is the entire decision, hidden in plain sight.
As a 20-year period-certain annuity: $659.96/month at 5%, $554.60 at 3%, $416.67 at 0% (the absolute floor — premium ÷ months). A real life annuity at 65 often pays more than these because of mortality credits: buyers who die early subsidize those who live long. That is why the right comparison is never the monthly check — it is the implied interest rate over your expected payout period.
Compute its implied rate: $650/month for 20 years on a $100,000 premium is a 4.82% internal rate of return. If 20-year Treasuries or top CDs yield more, self-annuitizing wins and the insurer keeps the spread. If the implied rate beats safe yields and you value the longevity insurance, it is competitive. Any agent who will not put the surrender schedule and annual fees in writing is telling you the implied rate cannot survive daylight.
Mortality credits. A period-certain annuity pays your money back with interest, full stop. A life annuity pools risk: the premiums of those who die early fund the checks of those who live past life expectancy, so survivors collect more than interest alone could pay. The trade: die early and the insurer keeps the remainder unless you bought a period-certain or refund rider — which lowers the monthly check by exactly the value of that guarantee.