A FIRE Calculator for People Starting a Business: What to Track

The first year of running your own business is where the standard FIRE calculator quietly stops applying to your life. Income is jagged, most of your net worth is locked inside one private company, and the U.S. Bureau of Labor Statistics reports that 20.4% of new private-sector establishments fail in their first year and 49.4% are gone within five.^[] A FIRE calculator for people starting a business has to deal with all three of those facts on the same screen — the savings rate that bounces month to month, the equity line that does not mark to market, and the survival probability that compounds against your timeline.

Most founders I know quietly use two numbers: a "good year" income they hope to repeat, and a private-equity valuation they would never quote to a buyer. Both are wrong inputs to a years-to-FI projection. The right inputs are net self-employment income smoothed over a rolling window, an explicit retirement-account contribution, and a separate, much more conservative bucket for the business itself.

Why a FIRE calculator for a new business owner needs different inputs

A salaried worker can plug a single gross-income number into any FIRE calculator and get a defensible answer because their savings rate, payroll-tax handling, and 401(k) match are all baked into one stable monthly cash flow. A founder has none of that. Owner draw is taxed as self-employment income — 15.3% on the first $176,100 of 2026 earnings before federal income tax even starts^[] — which means a "$80,000 net" founder is not the financial equivalent of an $80,000 W-2 employee.

The retirement-account choice does most of the damage. A SEP IRA caps the founder at roughly 20% of net self-employment income (the practical version of the 25%-of-compensation rule for sole proprietors), while a Solo 401(k) layers a $23,500 employee deferral on top of the same employer slot in 2026.^[] At sub-$100K net, the ceiling is what's binding — not how disciplined you are.

The numbers that actually move your years-to-FI

Three real numbers, three sources, and one calculation. The 2026 Solo 401(k) employee deferral limit is $23,500, with a combined cap of $71,500 for founders under 50.^[] The 2026 quarterly estimated-tax deadlines are April 15, June 16, September 15, and January 15, 2027^[] — miss one and the underpayment penalty is currently the federal short-term rate plus 3%, accruing at roughly 0.5% per month on the shortfall.

The 2024 BizBuySell median small-business sale price was $300,688, on an average revenue multiple of 0.67x and an average seller's-discretionary-earnings multiple of 2.49x.^[] That last number is what tells you whether your mental "the business is worth a million dollars at exit" passes a market sanity check.

The calculation rendered below holds personal expenses and net SE income constant at a realistic founder profile and varies only the retirement vehicle. The SEP IRA path takes about 29 years to FI; the Solo 401(k) path takes about 18. That eleven-year gap is not produced by working harder, charging more, or spending less. It is produced by filing one extra form.

What I actually track in the first 18 months

For the first eighteen months of a new business, I run a four-line dashboard that no general-purpose budgeting app gives you out of the box. Each line maps to a recurring decision a founder actually makes — not a category total to admire at the end of the month:

1. Owner draw smoothed against a rolling three-month average, so the savings-rate denominator does not lurch around with one good invoice.
2. Quarterly tax reserve, swept from every inflow into a tagged bucket on the day money lands — the easiest miss is letting the April number ride the operating account.
3. Retirement contribution as a percentage of net SE income, tracked against the SEP or Solo 401(k) ceiling, not against a generic "save 20%" target.
4. Business equity, marked at a defensible multiple, with the calculator deliberately excluding it from the FI assets line until an actual buyer is at the table.

Before any of that is worth doing, the near-term sinking funds for a first-year founder — quarterly tax reserve, six-month operating runway, and health insurance premium — need to be solved. FIRE math is downstream of not running out of money in month nine.

How MFFT models it

MFFT splits the problem deliberately. The FIRE calculator runs against your liquid invested assets only — brokerage, IRA, Solo 401(k), HSA — using your real-return and SWR assumptions to produce a years-to-FI number you can audit. The net worth tracker runs against the full balance sheet including business equity, but holds it at a manually-entered conservative valuation, so a flattering exit multiple does not silently shorten your apparent timeline. When a real liquidity event happens, you flip the equity into the invested-assets line and the FIRE projection updates honestly.

The two views never share a number, and that is the point. The FIRE projection is the floor — what you would reach with zero credit for the business. Any actual exit moves the date earlier; nothing about the projection requires the exit to materialize.

When this advice doesn't apply

If you are pre-revenue, on a sub-market salary at a venture-backed company, or holding restricted equity that won't vest for years, the relevant number isn't years-to-FI. It is months of personal runway weighted against the survival probability of the venture. The standard SWR math assumes diversified, marketable assets; a vesting cliff and a single concentrated stake do not satisfy either condition.

Treat this page as the playbook once net SE income is high enough to actually fund a SEP or Solo 401(k). Below that line, what matters is not slipping into credit-card debt while the business gets to revenue.

The takeaway I'd write on the back of a business card: smooth the income, separate the tax, max the right retirement vehicle, and keep the business equity off the FIRE line until somebody else has signed for it.