Coast FIRE Calculator for Couples

To use the Coast FIRE calculator for couples, enter your household's combined numbers: shared retirement spending, both partners' invested assets, and both partners' monthly contributions. The result is your joint Coast FIRE number: the amount the two of you need invested today so your combined portfolio grows into a full retirement fund without more saving.

1. Enter the older partner's Current Age. The calculator uses one timeline, so anchor it to one person. The older partner usually hits retirement first.
2. Set Retirement Age as the older partner's age on your planned joint retirement date. If Sam is 34 and Alex is 31 and you both want to stop when Sam is 62, enter 34 and 62. The calculator only needs the 28 years between now and then.
3. Enter your combined Annual Spending in Retirement. Use one household budget, not two personal budgets. Shared housing, utilities, and insurance mean a couple usually spends far less than twice what a single person spends.
4. Enter combined Current Invested Assets. Add both partners' retirement accounts and brokerage accounts, whether they're joint or individual.
5. Enter your combined Monthly contribution. Add both partners' contributions and any employer matches.
6. Check Advanced Settings. Use one set of assumptions for growth, inflation, and withdrawal rate. If one partner invests far more conservatively, use a blended growth rate.

How to read your results

• Coast FIRE number: what your household needs invested today.
• Progress: your combined balance as a share of that number.
• FIRE Nest Egg: the joint portfolio needed on your retirement date.
• Coast Age: the older partner's age when your household can stop saving. Subtract the age gap to get the younger partner's age.
• Cash Freed: the combined yearly saving you both get back.
• Real Return: your shared growth rate after inflation.

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The Coast FIRE calculator for couples treats your household as one investor. It finds the joint nest egg your shared spending needs, then discounts it by your real return over the years until you both retire.

The formula

FIRE Nest Egg     = Household Annual Spending ÷ Safe Withdrawal Rate
Real Return (r)   = (1 + Growth Rate) ÷ (1 + Inflation Rate) − 1
Coast FIRE Number = FIRE Nest Egg ÷ (1 + r)^Years

Worked example

Sam is 34 and Alex is 31. They want to retire together when Sam turns 62 and Alex turns 59, spending $70,000 a year. They leave Social Security out, since they'll retire before full retirement age.

1. FIRE Nest Egg: $70,000 ÷ 0.04 = $1,750,000
2. Real Return: 1.07 ÷ 1.03 − 1 = 3.88%
3. Growth factor over 28 years: 2.906
4. Coast FIRE number: $1,750,000 ÷ 2.906 = $602,191

Sam has $110,000 invested and Alex has $70,000, so together they hold $180,000, or 30% of their number. Sam saves $1,400 a month and Alex saves $1,100, a combined $2,500. The household reaches Coast FIRE when Sam is 55 and Alex is 52. Run separately, each partner's half of the plan would look different, but together their combined savings decide the date.

Factors that change your result

• Different retirement dates. If one partner plans to stop years earlier, run the calculator twice: once for each date. The earlier date gives a larger, more cautious Coast FIRE number.
• Separate finances. Couples who keep money separate can still use combined inputs. The result shows the household position, not who owns what.
• Shared spending. Your household budget should include costs that change in retirement, such as two people's healthcare before Medicare at 65.
• Rounding. Results are rounded to whole currency units, contributions are added yearly, and Coast Age is shown in whole years.

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