An annuity turns a capital sum into a stream of payments that continues for life. The income it offers is higher than the same sum could safely produce alone, and the reason is pooling.
Mortality pooling is the mechanism
An insurer selling annuities to many people knows roughly how long the group will live in aggregate, even though no individual outcome is predictable.
Payments to those who die early fund continued payments to those who live long. The pool transfers resources from short lives to long ones.
That transfer is what allows the income to exceed a sustainable withdrawal from an equivalent portfolio, since a portfolio must be sized for the possibility of a very long life.
Interest rates set the other half of the price
The insurer invests the premium, typically in bonds matched to the expected payment schedule, and the yield available determines how much income the sum can support.
Higher prevailing rates therefore mean higher annuity income for the same capital, and rates at the moment of purchase are locked in for the life of the contract.
This makes the timing of purchase consequential in a way that is not obvious, since the decision fixes a rate that cannot be revisited.
Features are paid for by reducing the income
An annuity that rises with inflation starts materially lower than a level one. A joint contract continuing to a surviving partner pays less than a single life version.
Guarantee periods, which continue payments for a minimum term regardless of death, similarly reduce the starting figure.
Each option removes some of the pooling benefit or lengthens the expected payment period, and the price adjusts accordingly.
Health information moves the price in the buyer's favour
Because the price depends on expected lifespan, conditions that shorten it can increase the income offered. This is the reverse of how underwriting works in most insurance.
Providers ask about medical history, smoking and sometimes postcode for exactly this reason, and quotes can differ substantially across providers on the same information.
Accepting the first offer without disclosure or comparison is the most common way buyers receive less income than their circumstances warrant.
The trade is flexibility for certainty
Once purchased, the capital is generally gone. There is no balance to draw on for an unexpected cost and usually nothing to leave to heirs beyond any guarantee.
In exchange, the income cannot run out and does not depend on market conditions, which removes the largest uncertainty in retirement planning.
Partial annuitisation covering essential spending, with the remainder invested, is the structure that addresses both concerns, though the right balance is personal and warrants advice.