Methodology
All calculators use standard financial formulas documented below. Each tool page links to the relevant section. Last updated: 2026-06-13.
We round display values for readability but compute internally at full precision. Tax tools use published bracket tables; mortgage tools use standard amortization unless noted otherwise.
SaaS runway
Runway (months) = Cash on hand ÷ Net monthly burn, where net burn = expenses − recurring revenue (if provided).
Customer acquisition cost (CAC)
CAC = Sales & marketing spend ÷ New customers acquired.
Lifetime value (LTV)
LTV = ARPU × (1 ÷ monthly churn rate) × gross margin. Churn entered as a monthly percentage.
Churn rate
Monthly churn = Customers lost ÷ Customers at start of period. Annual churn derived by compounding monthly rate.
Break-even
Break-even units = Fixed costs ÷ (Price − Variable cost per unit).
US mortgage payment
Standard fixed-rate amortization: M = P × [r(1+r)^n] ÷ [(1+r)^n − 1], where P = loan principal, r = monthly rate, n = number of payments.
Refinance break-even
Break-even months = Closing costs ÷ Monthly payment savings (when savings > 0).
UK mortgage
Repayment uses the same amortization formula as US fixed-rate loans. Interest-only payment = loan × annual rate ÷ 12.
UK stamp duty (SDLT)
Progressive bands for England & Northern Ireland. First-time buyer relief applies up to £625,000. Additional property surcharge +3% on each band. Source: GOV.UK SDLT.
Canada mortgage
Payments amortized over the full period (e.g. 25 years) while the rate is fixed for the term (e.g. 5 years). Balance after term reflects principal paid during the fixed period.
CMHC insurance premium
Premium bands by down payment: 15–19.99% → 2.8%, 10–14.99% → 3.1%, 5–9.99% → 4.0%. Premium added to loan when down payment < 20%. Source: CMHC.
US 1099 / self-employment tax
Net profit = gross 1099 income − expenses. SE tax = 92.35% of net × 15.3% (SS capped at wage base). Federal income tax uses 2025 single brackets and standard deduction minus 50% of SE tax. California state tax uses FTB progressive brackets when selected. Quarterly estimate = (total tax − withholding) ÷ 4.
UK Self Assessment
Income tax on profits minus personal allowance (£12,570, tapered above £100k). Class 4 NIC: 6% on profits £12,570–£50,270, 2% above. Payment on account = 50% of bill when tax > £1,000.
Canada self-employment (T2125)
CPP on pensionable earnings (11.9% combined rate). Federal and Ontario provincial tax on net income minus half of CPP. Quarterly instalment = total estimated tax ÷ 4.