How we calculate

Shared principles

No AI arithmetic. Every number comes from fixed, tested formulas. Auntie Randie's jokes follow simple rules and never change the results.

No double counting. We separate the cash that leaves your account from the true economic cost. Repaying a loan isn't a cost in itself, and money you've already spent isn't added to what's still to come.

South African benchmarks

• Investment return: 12.5% a year — a conservative long-term SA equity return. We use it wherever we show what money could have grown into.
• Inflation: 5.5% a year — a long-term SA CPI benchmark, used to step up future recurring costs such as habits.
• Interest rate: 12.75% — illustrative, not a current market rate.

Future value of monthly saving = Σ contribution × (1 + 12.5%/12)^(months remaining)
In today's money               = future amount ÷ (1 + 5.5%)^years

Data sources and labels

Energy prices use dated South African source references, not a live feed. Other defaults are Illustrative estimate estimates and every one is editable. Your saved inputs are never overwritten when reference prices change.

Treat all results as education, not financial advice.