The mechanics
Short notes that sit next to the engines. Skip anything you already know.
Interest vs Currency Debasement
Nominal growth is not purchasing power. Interest expands a balance; debasement erodes the unit.
Opens: Compound Engine
The Power of Compounding
Returns on returns. Frequency, contributions, and time turn a linear path into a curve.
Opens: Compound Engine
Nominal vs Real Returns
The number on the statement is nominal. Wealth is what that number still buys.
Opens: Compound Engine, Runway Matrix
Primary Drivers of Inflation
Demand-pull, cost-push, and monetary expansion — three mechanisms, one erosion of cash.
Opens: Runway Matrix, Compound Engine
Avalanche vs Snowball
Highest rate first versus smallest balance first. Same budget, different interest paid.
Opens: Debt Payoff Engine
Section 24 and BTL Tax
UK landlords cannot deduct mortgage interest in full. Model the 20% credit and SPV alternative.
Opens: Buy-to-Let Yield
ISA versus GIA Tax Drag
Identical portfolios, different tax. Dividend tax, CGT and turnover compound into a silent leak.
Opens: ISA / GIA Optimiser
FIRE Number and Safe Withdrawal
Annual spend divided by a withdrawal rate is the target. Savings rate sets the date.
Opens: FIRE Matrix
Emergency Runway
Fixed burn is survival. Variable burn is lifestyle. Dependants and income risk stretch the target.
Opens: Runway Matrix
Unit Economics and Billable Time
Price minus variable cost funds fixed cost. Unbillable hours are a tax on every hour you sell.
Opens: Billable Rate Engine, Break-Even Engine
Salary, Dividends and Corporation Tax
A low salary near the NI threshold plus dividends is the classic UK director split — until bands move.
Opens: Dividend / Salary Splitter
The Empire Lab
A paper empire that forces the same choices the engines quantify: cash vs assets, heat vs yield, wages vs growth.
Opens: Compound Engine, FIRE Matrix, ISA / GIA Optimiser