Coast FIRE for couples: one future, two timelines

Coast FIRE as a couple is not two single plans stapled together. Your spending is joint, your portfolio is effectively one pot, and your timelines are probably different. Here is how to run the numbers as a household without fooling yourselves.

Start with one number, not two

Your coast number is based on what the household will spend in retirement, not on what each of you spends now. Add up the joint annual spending you expect, multiply by 25 for the 4% rule target, then ask how much you need invested today so growth alone reaches that target by your chosen age. The coast FIRE calculator does this; run it on household numbers. If your savings sit in different accounts and wrappers, add them together for this question. Compounding does not care whose name is on the account.

The two-ages problem

Couples are rarely the same age, and "retire at 60" means two different years. Pick one target date for the joint number, usually when the younger partner reaches the chosen age, because that is the conservative reading of "we both stop." In the US there is a second wrinkle: penalty-free withdrawals from retirement accounts generally start at 59 and a half, so if one of you is much older, the older partner's accounts can bridge the years until the younger partner's unlock. That sequencing detail is worth an hour with a fee-only planner, because the tax rules around who withdraws what, and when, are where couples most often leave money on the table.

The most common pattern: one coasts, one anchors

In practice, few couples flip the coast switch on the same day. The usual story is that one partner's income covers all household expenses, which frees the other to leave a draining job years early, work part-time, or handle the unpaid work that makes the plan cheaper, like cooking and childcare. The household is coasting even though one person still has a career. This only works if the anchoring partner's job is sustainable and insured, which is why the part-time benefits list matters for couples too.

A worked example

A couple, both 34, spends $70,000 a year and has $400,000 invested. The full target is 25 times spending: $1,750,000. At a 5% real return, $400,000 grows to that in about 30 years, reaching it around age 64 with nothing more added. They have been coasting since today and never noticed. If they want the finish line at 60 instead, they need roughly $490,000 today, or they keep saving a little for a few more years and coast from there. The point of running the joint number early is that many couples discover the pressure to save can drop years before the pressure to work can.

Rules that keep it honest

Re-run the numbers together once a year, because markets and spending both move. Agree in advance what happens in the bad case: if the portfolio falls well behind the coast path, who raises income and by how much. And keep one emergency fund for the household; two people drawing on separate cushions double-count security.