Coast FIRE Calculator for Couples
Plan Coast FIRE as a household. Enter each partner's age, invested assets and contributions, set one shared retirement spending target, and see whether your combined investments can coast to retirement.
Partner A
Partner B
Shared household assumptions
Household FIRE number
$1,500,000
Combined coast projection
$944,820
Shortfall at retirement
$555,180
The coast projection grows your current combined assets to age 65 with no further contributions. If you keep contributing, you are projected to reach $1,979,790.
Partner A
33 years to retirement · grows to $400,255
Partner B
31 years to retirement · grows to $544,565
How Coast FIRE works for a couple
A couple shares most fixed costs - housing, utilities, subscriptions - so two people rarely spend twice what one person does. That is why this calculator asks for a single household retirement spending figure rather than doubling an individual number. From that it derives one household FIRE number, grows each partner's current investments forward to your shared target retirement age, and adds them together. If the combined total reaches the household FIRE number with no further contributions, you have reached Coast FIRE as a couple.
Why couples don't need 2x the money
The single biggest mistake couples make with FIRE math is doubling a single person's number. Shared housing, utilities, transport and subscriptions mean a two-person household typically spends roughly 1.4 to 1.6 times what one person spends, not double. Because your FIRE number is just annual spending divided by your withdrawal rate, that shared-cost discount flows straight through: a couple spending $60,000 a year needs a $1.5M nest egg at 4%, not the $2M that two separate $40,000 singles would need. Entering one honest household budget is the most important input on this page.
How two different ages are handled
Partners are often different ages, which changes how long each person's money compounds. This calculator grows each partner's investments separately - from their own current age to your shared target retirement age - and then sums the two projections. A 30-year-old's $80,000 has 35 years to compound; a 38-year-old's $120,000 has 27. Treating them separately and adding the results is more accurate than averaging your ages, and it shows clearly how the younger partner's longer runway pulls more weight.
The coast test: stop contributing today
Coasting means your existing investments can grow to your target on their own, without another dollar saved. So the headline figure here is the combined coast projection - both partners' current assets grown to retirement age with no further contributions. If that already exceeds your household FIRE number, you have coasted: you could both stop investing for retirement and still arrive on target. If it falls short, the calculator also shows your projection if you keep contributing, so you can see how close ongoing saving gets you.
When one partner has saved far more
Couples rarely have matching balances, and that is fine - Coast FIRE works on the household total, not a per-person split. A partner who started earlier or earned more may carry most of the combined projection, and the household can still coast even if the other partner has very little invested. What matters is whether the two projections together clear the shared target. The calculator keeps each partner's inputs visible so you can see the balance, but the coast decision is always made at the household level.
Sources & methodology
- Trinity Study (1998) — evidence base for the 4% safe withdrawal rate
- S&P 500 historical returns — basis for the long-run ~7% real return assumption