01Mortgage and real estate math

Monthly principal and interest uses the standard amortization formula M = P × [r(1+r)^n] / [(1+r)^n − 1], where r is the annual rate divided by 12 and n is the term in months. Amortization schedules are generated month by month so extra principal payments and payoff dates are exact.

PITI adds monthly escrow for property tax and homeowners insurance using state effective rates: property tax ranges from 0.28% (Hawaii) to 2.23% (New Jersey) of home value annually; insurance ranges from roughly 0.38% to 1.35%. PMI is priced as an annual percentage of the loan amount based on credit tier and LTV, and is removed once the balance reaches 78% of original value.

Affordability mode solves for the maximum loan such that P&I plus escrow stays within the selected front-end DTI, then adds existing monthly debt for the back-end check.

Rent vs buy projects two net-worth paths annually: the buy path appreciates the home, amortizes the loan and deducts 6% selling costs; the rent path invests the down payment and any monthly cash-flow difference at the selected market return. Break-even is the first year the buy path exceeds the rent path.

02Payroll and income tax

Federal income tax applies 2026 marginal brackets (10/12/22/24/32/35/37) to taxable wages after pre-tax deductions and the standard deduction ($16,100 single, $32,200 joint, $24,150 head of household).

FICA uses 6.2% Social Security up to the 2026 wage base of $184,500 and 1.45% Medicare, plus the 0.9% additional Medicare tax above $200,000 single / $250,000 joint. State tax applies a state effective rate, not full state brackets, and local city taxes are not modeled.

Self-employment tax uses 15.3% on 92.35% of net self-employment income, with half deductible above the line. The QBI deduction is modeled at 20% of qualified income for filers under the 2026 thresholds.

Capital gains apply 0/15/20 long-term brackets stacked on ordinary income, ordinary rates for short-term gains, 28% for collectibles, and the 3.8% net investment income tax above $200K/$250K MAGI.

03Retirement and debt

401(k) projections compound annually: each year adds employee contributions (capped at $24,500), employer match (capped by your match formula), and growth on the prior balance. Retirement income uses the 4% withdrawal rule.

Student loan comparisons implement the current federal formulas: RAP at 1%–10% of AGI in $10,000 bands, less $50 per dependent, with a $10 floor and 30-year forgiveness; PAYE at 10% of AGI above 150% of the poverty guideline; and IBR at 15% above 150%. IBR and PAYE are capped at the Standard 10-year payment, RAP is not. SAVE was vacated in March 2026 and is no longer offered.

Debt payoff simulates month by month: interest accrues on every balance, minimums are paid, then all surplus goes to the target debt ordered by balance (snowball) or rate (avalanche).

04Business metrics

SaaS company value uses SaaS Capital’s published model: multiple = −3.2 + 0.32 × SCI + 8.26 × ARR growth + 2.62 × NRR, with growth and NRR as decimals. The separate custom EV/ARR method uses the visitor’s multiple, then subtracts debt and adds cash for equity value. Rule of 40 = signed growth % + profit margin %; burn multiple = net burn ÷ net-new ARR; S&M payback = annual S&M ÷ (net-new ARR × gross margin) × 12.

EBITDA adds interest, taxes, depreciation and amortization to net income. SDE additionally adds owner compensation and non-recurring expenses, then deducts a market replacement salary so a buyer can see the absentee-owner benefit.

Freelance rate separates after-tax personal costs from deductible business costs: minimum revenue = deductible costs + personal costs ÷ (1 − effective tax rate). The quote applies the chosen markup or margin, then rounds up. Project labor uses that quote, with rush on labor and direct expenses added separately.

LTV:CAC uses same-period marketing plus sales spend divided by new customers. Subscription cohorts compound logo survival and surviving-account expansion, then apply gross margin and optional discounting; nonconvergent paths are labeled horizon-capped. Known-lifetime and repeat-purchase models use their own finite-lifetime formulas. Simple, cumulative-cohort and discounted-cohort payback remain distinct.

Burn runway separates static cash ÷ current net burn from a monthly path that compounds revenue and expenses, applies planned hiring and adds financing only to cash. Cash depletion, durable operating break-even, funding-dependent break-even and horizon-capped outcomes are distinct. Target cash uses the lowest interim balance; the optional burn multiple uses net burn and net-new ARR over the same forward 12 months and requires an explicit recurring-revenue basis.

05Data sources

Figures are sourced from public data and refreshed on the following cadence:

• Mortgage and macro rates: Federal Reserve FRED series (MORTGAGE30US, MORTGAGE15US), refreshed daily.
• Federal tax brackets, standard deduction and FICA limits: IRS revenue procedures for tax year 2026.
• Freelance tax context: IRS self-employment tax and self-employed retirement contribution guidance; the rate tool uses an entered effective rate rather than preparing a return.
• Conforming loan limits: FHFA annual announcement ($806,500 baseline for 2026).
• State income tax: state revenue department publications, modeled as effective rates.
• Property tax and insurance: state assessor and insurance department averages.
• SaaS valuation: SaaS Capital’s 2022 private-company framework and SaaS Capital Index; bundled SCI 4.22× is rounded from the official 2026-09-30 workbook observation, not a live feed.
• Burn definitions and runway: Carta and Brex; default-alive framing: Paul Graham; net-new ARR and cash-efficiency context: Bessemer Venture Partners. Burn scenarios use visitor inputs rather than a live benchmark feed.
• LTV and acquisition definitions: Stripe and Shopify; cohort modeling context: David Skok; retention and cash-efficiency context: Bessemer Venture Partners. All LTV:CAC outputs use visitor inputs rather than live benchmark data.
• Cost of living: regional price parities, reweighted across six categories.
• LLM pricing: provider price pages, reviewed monthly.
• Nutrition: Mifflin-St Jeor (PMID 2305711), revised Harris-Benedict (PMID 6741850) and Katch-McArdle from McArdle, Katch and Katch; USDA 4/4/9 energy factors and adult AMDR references; ISSN protein position stand (PMID 28642676); FDA fiber reference of 14 g per 1,000 kcal. Activity and goal percentages are planning assumptions, not prescriptions.

06Known limitations

State income tax is modeled as a single effective rate rather than full brackets, so high earners in progressive states will see slight differences from a CPA-prepared return. Local and city taxes are excluded.

Cost-of-living indices are metro-level averages; your actual cost depends on neighborhood, housing tenure and household composition. Insurance assumptions are state averages and do not reflect individual property risk.

SaaS model outputs are illustrative and extrapolation outside the published input or output domains is flagged. Custom multiples are visitor assumptions. Neither method is an appraisal, offer or complete transaction model.

Burn projections are deterministic monthly scenarios, not accounting forecasts. Collection timing, seasonality, taxes, debt service, restricted cash and unentered one-time events can change actual depletion and break-even outcomes.

LTV:CAC assumes constant entered churn, expansion, margin and revenue within each model. Cohort history, sales lag, purchase timing, channel mix and overhead can materially change actual LTV and payback; a ratio is not company profit or a forecast.

Macro results are predictive-equation estimates for healthy adults 18+, not measurements or medical nutrition therapy. Body-fat error affects lean-mass calculations; activity and goal multipliers are assumptions; AMDR comparisons are not health grades; a static calorie gap is not a weight-change forecast. Meal calories use rounded gram targets and disclose their rounding difference.

07Change log

November 2026: rebuilt Macro Calculator with exact US/metric conversion, three disclosed resting-energy equations, custom calorie and macro modes, infeasible-split warnings, AMDR and fiber context, conserved meal rounding and an adult health-scope notice.

November 2026: rebuilt LTV:CAC with three fit-specific models, nonconvergent and zero-denominator handling, discounting, cumulative payback, target CAC, sensitivity scenarios and monthly exports.

November 2026: corrected Burn Rate’s break-even/zero-cash conflation, added funded and horizon-capped outcomes, hiring and target solvers, and required matching-period recurring revenue for burn multiple.

November 2026: replaced the opaque SaaS growth-band score with the sourced SaaS Capital model, added custom EV/ARR and equity bridging, corrected Rule of 40, and added nullable efficiency and fundraising diagnostics.

October 2026: refreshed 2026 tax brackets and standard deductions, replaced the ended SAVE plan with RAP, added rate stress tests to the mortgage tool, revised LLM pricing table.

August 2026: rebuilt cost-of-living weights, added state insurance rates for Florida and Louisiana repricing.

June 2026: launched image compressor with browser-only processing.