How much to annuitize

A significant proportion of Americans are living longer than they anticipated. An income annuity is designed to protect against outliving one's assets. Mark Hulbert answers the question: "Do annuities have a place in your retirement portfolio?" Jeffrey Brown, Dean of the College of Business at the University of Illinois at Urbana-Champaign and director of the Retirement Research Center of the National Bureau of Economic Research describes the role of annuities: “the entire point of an annuity is to insure against longevity risk.”
"What is the right amount to allocate to annuities in your retirement portfolio? The answer, as you can imagine, depends on a whole host of assumptions."
"One clue comes from an analysis conducted by David Blanchett, head of retirement research at Morningstar. His focus was on deferred-income annuities, which differ from SPIAs in that their guaranteed payment begins at a later point. After analyzing more than 78,000 possible scenarios, each one of which represents a different series of assumptions, Blanchett found that the average optimal allocation across all scenarios was 30.52%."
https://www.marketwatch.com/story/do-annuities-have-a-place-in-your-retirement-portfolio-2018-11-14