Starter FI Math Walkthrough
One worked example you can copy
Here is a complete worked example with real numbers. Follow along with your own figures substituted in, and you will have a genuine financial independence estimate by the end rather than a vague sense of the concept.
Step one: establish actual spending
Our example household takes home $7,000 a month and spends $4,500 of it. That spending figure comes from twelve months of real transactions, not from a budget they wrote once.
Annual spending is therefore $54,000. This is the number everything else depends on, which is why it is worth getting right.
Their savings rate is the remaining $2,500 a month, which is about 36% of take-home pay.
Step two: calculate the target
At a 4% withdrawal rate, the target is $54,000 times twenty-five, which is $1,350,000.
Because they are in their mid-thirties and planning for a long retirement, they also calculate a cautious version at 3.5%, giving $1,542,000.
They decide to plan toward the cautious figure and treat the lower one as an early-finish possibility rather than the goal.
- Annual spending: $54,000 from real transaction history.
- Savings rate: $2,500 a month, roughly 36% of take-home pay.
- Target at 4%: $1,350,000. At 3.5%: $1,542,000.
- Starting portfolio: $120,000 across all accounts.
- Estimated timeline: somewhere around eighteen to twenty years at 6%.
Step three: count what you already have
They total every account: a current 401(k), an old one from a previous job, an IRA, and a small taxable brokerage balance. Together it comes to $120,000.
Their emergency fund is deliberately excluded, because that money has a different job and should not be counted toward financial independence.
That $120,000 is the starting balance for the projection, and it does considerable work over two decades on its own.
Step four: find the timeline
With $120,000 invested, $2,500 a month added, and a 6% assumed return, they reach the cautious target in roughly eighteen to twenty years.
They run it at 4% as well, which extends the timeline by several years. That version is the one they treat as the realistic downside.
Both numbers go in a note with the date, so next year's review has something concrete to compare against.
A detail the simple math skips
Most of their $120,000 sits in retirement accounts, which have age restrictions on withdrawals. Retiring in their early fifties means they need money accessible before then.
The usual solution is building a taxable brokerage balance alongside the retirement accounts, so there is a bridge covering the years before penalty-free access begins.
There are established strategies for accessing retirement funds early, and they add complexity. A taxable account is the simpler path for most people.
They decide to direct a portion of future contributions to a taxable account for exactly this reason, which slightly reduces the tax benefit and considerably increases their flexibility.
Step five: decide what to adjust
Eighteen years feels long, so they test the levers. Cutting $500 a month from spending lowers the target by $150,000 and raises savings, which removes several years.
Raising income by $500 with spending unchanged helps less, though it is easier for them in practice given their careers.
They settle on a combination: a modest housing change, redirecting the next two raises, and accepting a timeline around fifteen years.
The plan gets written down with actual numbers and a reminder to revisit it each January with updated balances.
Try these inputs
- The example: $120,000 start, $2,500/mo, 6%, target $1,542,000
- Conservative return: same inputs at 4%
- After a spending cut: $3,000/mo saved, target $1,400,000