Methodology
Engines run in your browser. Models update when UK tax rules change. This page is the contract: what we compute, and for which tax year.
Principles
Engine notes
Compound Engine
Future value of principal plus recurring contributions, with compounding frequency, optional deposit step-up, and inflation converted to real purchasing power.
FIRE Matrix
Target = annual spend / SWR. Portfolio grows at a real return plus savings until the target, capped at 60 years.
Debt Payoff Engine
Avalanche (highest APR) versus snowball (smallest balance), compared with a minimums-only baseline. Extra payment is snowballed onto the active target.
Buy-to-Let Yield
UK SDLT bands including additional-dwelling surcharge, Section 24 20% finance-cost credit for individuals, and corporation tax for SPVs. Rate-stress reruns interest, tax and ROCE.
ISA / GIA Optimiser
ISA grows tax-free. GIA applies dividend tax and CGT on turnover each year, plus a terminal CGT on unrealised gains. 2026/27 allowances: £500 dividends, £3,000 CGT.
Runway Matrix
Target reserve = risk-adjusted monthly burn × months. Risk-adjusted burn uses 30% of variable spend, an income-risk multiple, and +5% per dependant.
Billable Rate Engine
Desired take-home is grossed up for tax, then overhead and profit margin, then divided by billable hours (hours/week × weeks/year).
Break-Even Engine
Break-even units = ceil(fixed / (price − variable)). Safety margin versus a chosen target volume.
Dividend / Salary Splitter
Salary deducted before corporation tax. Employee NI 8%/2%. Dividend tax 8.75%/33.75%/39.35% after £500 allowance and unused personal allowance. Personal allowance £12,570.
Whorton Empire
Deterministic paper-empire with stochastic events. Collection applies wages, inflation on cash, fund marks, heat, and optional audits. Not a model of real criminal activity.
HMRC parameter audit
Tax year 2026/27- All engines last verified: 2026/27
- Section 24, dividend allowance, CGT annual exempt amount, income tax and NI bands checked against published HMRC rates
- Next scheduled review: April 2027, or sooner if mid-year rules change
Disclaimer
These tools are for information and education. They are not financial, tax or investment advice. Verify figures against official sources and consult a qualified professional before acting.