Coast FIRE for Couples: How to Run the Numbers Together

Most Coast FIRE calculators, ours included, ask for one age and one balance. If you’re planning with a partner, that can feel like half the picture is missing. It isn’t. You just have to enter household numbers instead of personal ones, and make one decision about timing.

Think in households, not individuals

Your portfolio doesn’t care whose name is on each account. What matters is how much the two of you have invested in total, how much you’ll spend together in retirement, and when the paychecks stop.

So when you use the calculator, “invested today” means both balances added together: 401(k)s, IRAs, invested HSA money and any taxable brokerage accounts. Leave out your emergency fund and your home equity. “Yearly spending” is what the household will spend, which for two people is usually well under double what one person would, since you share housing and a lot else. “Monthly contribution” is everything both of you put in.

If you’d rather split things down the middle, that works too, with one condition. Two people who each plan to spend $40,000 a year and stop working at the same time each have a Coast FIRE number of $318,862. Add those together and you get exactly the household number for $80,000. The math only diverges when your timelines do.

What to do about an age gap

The calculator doesn’t really care about age. It cares about the number of years until your portfolio has to start paying the bills.

Say one of you is 32 and the other is 29, and you plan to stop working together when the older one turns 62. That’s 30 years either way. You can enter 32 and 62, or 29 and 59, and you’ll get the same result.

It gets trickier if you won’t stop at the same time. If the younger partner keeps working for three more years, their paycheck covers part of your spending for that stretch, and your portfolio gets three more years to grow. The simple, slightly conservative approach is to use the date the first of you stops working. You’ll overshoot a little, and overshooting is the better mistake to make with retirement money.

A worked example

Alex is 32 and Priya is 29. They have $210,000 invested between them, $140,000 in Alex’s accounts and $70,000 in Priya’s. They expect to spend about $80,000 a year once they both stop working, and they’re aiming for that when Alex turns 62.

Their FIRE number is $80,000 ÷ 4% = $2,000,000. With 30 years to go, 7% returns and 3% inflation, their Coast FIRE number is $637,725. They’re about $428K short today.

How fast they close that gap depends almost entirely on what they put in each month:

Going from $2,000 to $3,000 a month moves their Coast FIRE date by 14 years. That’s the single most useful thing a couple can take from this calculator: below a certain monthly amount you’re barely outrunning the target, and a little above it you buy back a decade or more.

When one of you wants to cut back

This is where Coast FIRE gets interesting for couples. Once the household crosses its number, retirement saving is finished. From then on you only need enough income to cover today’s life, which can mean one of you goes part-time, goes back to school or stays home with kids while the other paycheck covers the bills.

Before that point it’s a much harder trade. If Alex and Priya dropped to $1,200 a month in contributions today, which is roughly what losing one income would do to their budget, they wouldn’t reach Coast FIRE before 62 at all. The same change made after they cross the line costs their retirement nothing.

If what you really want is for both of you to work less soon, and for your investments to start covering some of your costs, that’s closer to Barista FIRE than Coast FIRE.

Accounts and other details for couples

A few things only apply when there are two of you:

• A spousal IRA lets a spouse with little or no income contribute to an IRA based on the other spouse’s earnings, as long as you file taxes jointly. It’s one of the easiest ways to keep contributions up when one income drops.
• If you both have a 401(k) match, get both matches before anything else. Nothing else gives you an instant return like that.
• Married couples can receive Social Security spousal benefits of up to half of the other spouse’s full benefit. That can lower the spending your portfolio has to cover, and our Social Security and pensions post shows how to count it.
• If the partner who plans to cut back is the one with the family health insurance, price replacement coverage into your spending before anyone hands in notice.

The conversation that matters most isn’t about accounts, though. It’s agreeing on the retirement spending figure. Couples who argue about money often disagree about that number without realizing it, and the calculator makes it concrete in a way a budget spreadsheet doesn’t.