Longevity math: planning income to 95 vs 100

Most retirement plans pick an end date: 90, 95, sometimes 100. The choice feels abstract, so people pick a round number and move on. But the difference between planning to 95 and planning to 100 is concrete. It is sixty more months of living costs. This file is about seeing that number clearly.

Why plan past life expectancy at all?

"Life expectancy" is an average. By definition, many people live past it. And the older you already are, the further out your own expected age goes, because you have already passed the risks that ended earlier lives.

Two free tools let you see your own range instead of a national average:

• The Social Security Administration's life expectancy calculator, which shows average additional years based on your sex and date of birth.
• The Longevity Illustrator from the Society of Actuaries and the American Academy of Actuaries, which shows the chance of reaching various ages, and lets you add a few health and lifestyle answers.

Run both. Notice that "the chance I reach 95" is not tiny, especially for a couple, where the question is whether either of you does. Plan for the long end, not the middle.

Step one: sort your income

Every income source goes in one of two columns.

Lasts as long as you do	Can run out
Social Security	Savings and checking
A traditional pension (check survivor terms)	IRAs, 401(k)s and other retirement accounts
A lifetime annuity	Brokerage accounts
	Rental income you might sell
	Part-time work

The left column is your floor. It keeps paying at 100. The right column is what you spend down to fill the gap.

Step two: find the monthly gap

Write down what you spend in a typical month. Subtract the left column.

monthly gap = monthly spending − lifetime income

That gap is what the right column has to cover, every month, until the end of the plan.

Step three: the five-year difference

Now the arithmetic that answers the title. Using made-up round numbers to show the method: say your monthly gap is $1,500.

Plan to age	Extra months beyond 95	Extra cost before inflation
95	0	$0
100	60	$1,500 × 60 = $90,000

Put in your own gap. Then remember two things that push the number in opposite directions:

• Inflation raises the cost. Those last five years are the furthest away, so prices will have risen the most by then.
• Spending often changes with age. Many people travel and spend less in their late 80s and 90s, but health and care costs can rise. Plan both ways and see how much each matters.

Levers that change the answer

You can't control how long you live. You can control these:

1. When you claim Social Security. Delaying past full retirement age earns delayed retirement credits up to age 70, which raises the monthly benefit for life. Social Security benefits also receive annual cost-of-living adjustments, which helps against inflation. A bigger lifetime benefit shrinks the monthly gap at 95 and at 100. Your own estimates are on your my Social Security account at ssa.gov.
2. The survivor benefit. For married couples, when the first spouse dies the survivor generally keeps the larger of the two Social Security benefits, not both. The household's lifetime income drops. Plan the survivor's budget separately.
3. Pension choices. If you have a pension, the choice between a single-life payment and a joint-and-survivor payment decides whether the income continues for a surviving spouse.
4. Converting savings into lifetime income. A lifetime income annuity turns a lump sum into payments for life, moving money from the right column to the left. It also gives up flexibility and access to that money. Weigh it carefully and read the contract.
5. Required withdrawals. Federal rules require minimum withdrawals from most tax-deferred retirement accounts starting at age 73, or 75 for people born in 1960 or later, under the SECURE 2.0 Act. Those withdrawals are not a spending plan. You can withdraw and save what you don't need.
6. The house. Home equity is often the largest reserve. Decide now whether it is part of the plan for your 90s, and how: selling, downsizing, or borrowing against it.

A simple test of your plan

Ask: "If I live to 100 and my savings run out at 92, what would my life look like on lifetime income alone?" If the answer is frightening, adjust now while the levers still work. If the answer is livable, you have a plan that holds to the end of this timeline.