1. Scope
Projects personal runway for a solo founder drawing on savings plus side income while MRR compounds. It does not model taxes precisely, investment returns on idle cash, or category-level cost-of-living inflation.
2. Inputs and outputs
Inputs
- savings number (currency)
Liquid runway at month zero.
- monthlyExpenses number (currency)
Personal living expenses plus any business costs not covered by MRR.
- sideIncome number (currency) default: 0
Steady side income (freelance, part-time).
- startingMrr number (currency) default: 0
- mrrGrowthRate percent default: 0
Month-over-month compounding growth.
Outputs
- monthsToRamen
Months until MRR + side income covers monthlyExpenses.
- monthsToFullyProfitable
Months until MRR alone covers monthlyExpenses.
- runwayMonths
Months before savings hits zero, net of shortfall each month.
- monthlyTrajectory
Array of per-month savings balance, MRR, net shortfall.
Engine source: src/lib/bootstrapped-runway-calculator/engine.ts
3. Formula / scoring logic
for month m = 1..horizon:
mrr_m = starting_mrr * (1 + growth) ^ m
shortfall = max(0, monthly_expenses - side_income - mrr_m)
savings_m = savings_{m-1} - shortfall
stop when mrr_m + side_income >= monthly_expenses (ramen-profitable)
stop when mrr_m >= monthly_expenses (fully profitable)
stop when savings_m <= 0 (cash-out)4. Assumptions
- MRR growth compounds monthly at a constant rate — no seasonality.
- Side income is steady. Irregular income should be averaged before entry.
- Taxes and one-offs (insurance, quarterly estimated tax) are captured inside monthlyExpenses or ignored.
5. Data sources
6. Known limitations
- Constant-growth MRR is optimistic past month 12. For longer horizons, consider a staged growth assumption (ramp → plateau) outside the tool.
- No tax engine: rough rule of thumb is to pre-tax expenses by 20–30% before entry, or use the Freelance Tax Estimator for the side-income line.
- Cash-out logic assumes savings are liquid. Home equity, retirement accounts, and locked instruments are not runway.
7. Reproducibility
Input
savings = 20000, monthlyExpenses = 3500, sideIncome = 1500, startingMrr = 200, mrrGrowthRate = 10%.
Expected output
Ramen-profitable at ~month 13 (MRR + side ≥ expenses); runway to cash-out ~month 14 at baseline.
8. Change log
- 2026-04-24 methodology page first published.