Coast FIRE for couples: how to work out one number for two people

Most Coast FIRE guides are written for one person. But many people plan their money as a couple: two incomes, two sets of retirement accounts, one shared life. This guide shows how to turn all of that into one Coast FIRE number you can both work towards.

If you want to try it as you read, open the calculator and choose Couple.

A quick reminder: what is Coast FIRE?

Coast FIRE is the point where the money you have invested will grow into your full retirement pot by itself. After that, you only need to earn enough to cover your life today. You no longer need to save for retirement.

For a couple, the question becomes: when do we have enough invested that we can both stop saving for retirement? If you are new to the idea, read What is Coast FIRE? first.

Think of yourselves as one household

The simplest way to plan as a couple is to treat yourselves as one household with one pot. That means adding things together.

Add together:

• Investments. Both of your retirement accounts, index funds and other long-term investments. Leave out your home and your emergency fund.
• Monthly saving. Everything both of you put into those investments each month, including any employer contributions.
• Pensions. Both of your expected pensions or Social Security, in today’s money.

Do not double:

• Spending. Enter what you expect to spend together each year in retirement. Two people sharing a home usually spend much less than twice what one person spends.

Whose age do you use?

The calculator needs one age for the timeline. It uses the first person’s age, which is yours.

If you are close in age, this hardly matters. If one of you is several years older, it is worth running the numbers twice: once with each age. Using the older partner’s age is the cautious choice, because it gives growth fewer years to work.

A worked example

Alex is 34 and Jordan is 31. They plan to retire at 65. Together they have $180,000 invested and add $1,500 a month. They expect to spend $70,000 a year in retirement, and between them they expect $24,000 a year from pensions.

Step 1: What does the pot need to pay? $70,000 − $24,000 = $46,000 a year.

Step 2: How big does the pot need to be at 65? At a 4% withdrawal rate: $46,000 ÷ 0.04 = $1,150,000.

Step 3: What is their Coast FIRE number today? With 7% growth and 3% inflation, real growth is 3.88% a year. Using Alex’s age of 34, that is 31 years of growth: $1,150,000 ÷ 1.0388^31 = $352,984.

With $180,000 invested, they are 51% of the way there.

Step 4: When can they stop saving? At $1,500 a month, they reach their Coast FIRE number when Alex is 47.

Alex and Jordan's path, using Alex's age

Money investedAmount needed to coast

$0$400K$800K$1.2M

Age 47 · $592,475

Can stop saving here

3440506065

If they plan around Jordan’s age instead, their Coast FIRE number today is $314,858 and they could stop saving at 41 on Jordan’s timeline. That is the difference three extra years of growth make. Using the older partner’s age is the safer plan.

The choice couples have that singles do not

Reaching Coast FIRE as a couple often opens up a very practical option: one of you can step back from work while the other keeps going.

Say Jordan wanted to cut back sooner and they could only save $900 a month instead of $1,500. With everything else the same, they would reach Coast FIRE when Alex is 60 instead of 47. That is a big difference, and it is exactly the kind of trade-off worth seeing in numbers before you decide.

When Alex and Jordan can stop saving

• Plan on Alex's age (34)Age 47
  13 more years of saving
• Plan on Jordan's age (31)Age 41
  10 more years of saving
• Save $900 a month insteadAge 60
  26 more years of saving

Once you have reached Coast FIRE, the picture changes. Neither of you needs to save for retirement any more, so the household only needs to earn enough to pay for today. That might mean one full-time income, two part-time ones, or a career change that pays less but suits you better.

Pensions: count them, carefully

Pensions make a huge difference to a couple’s number, because they reduce what your investments need to pay. In the example, $24,000 a year of pensions cut the pot needed at 65 from $1,750,000 to $1,150,000.

A few cautions:

• Only include pensions you are confident about. Check official forecasts where you can, such as your Social Security statement or State Pension forecast.
• Enter them in today’s money.
• If one pension starts later than your retirement age, use a lower figure for now.

Coast FIRE with a pension or Social Security goes into this in more detail.

What if you keep separate finances?

Plenty of couples keep some or all of their money separate. You can still use one household number for the shared goal, then decide between you how to split the saving. Or you can each run the calculator as Just me, with your own investments and your share of the spending. Both approaches are fine. The household version is usually more realistic, because in retirement most couples share their costs.

Track it together

The most useful thing a couple can do is look at the number together once a month. It takes a minute: what are our investments worth now, and what did we add? The Track section of the calculator does this and shows whether your stop-saving age moved.

Your plan is saved in your browser only, so if you both want to see it, use the backup button to share the file between your devices.

Work out your number as a couple

Find your Coast FIRE number as a couple. Choose Couple, enter your household totals, and see the age you can both stop saving.

This article is for education, not financial advice. All figures are in today’s money and do not include taxes or fees.