A Boston mutual fund company is adding a variable annuity feature than can convert retirement savings into a guaranteed lifetime income stream for married couples.

The company, Pioneer Investments, says it will be offering single and joint lifetime income options to purchasers of its AnnuiStar Variable Annuity contracts.

The riders, the Living Income Guarantee rider and the Living Income Guarantee for 2 rider, will offer a guaranteed minimum withdrawal benefit for life.

Couples can use the rider to convert an individual retirement account into a lifetime income stream for both a husband and a wife, Pioneer says.

Purchasers who put off making withdrawals can receive withdrawals of up to 7% of the amount invested, Pioneer says.

Travelers Life & Annuity Company, a unit of MetLife Inc., New York, is backing the Pioneer rider guarantees.