Quick guide
How to use this calculator
- Enter one scenario with a consistent currency and the exact time basis shown by each label.
- Treat growth, return, price change, and future contributions as assumptions rather than forecasts.
- Use the component results and calculator-specific boundary to interpret the primary answer.
Calculation method
Calculation method
Income change = current income − prior income; spending change = current spending − prior spending; absorbed share = spending change ÷ positive income change.
Exact rational arithmetic is used where no compounding is needed. Bounded projections use stable logarithmic growth, deliberate decimal display rounding, overflow checks, and explicit unreachable states; a nonzero result is never replaced by zero.
Worked example
Worked example
Income rising from 4,000 to 5,000 while spending rises from 3,000 to 3,600 means 600, or 60%, of the additional 1,000 went to higher spending.
Income change = current income − prior income; spending change = current spending − prior spending; absorbed share = spending change ÷ positive income change.
Supported inputs
Precision and limits
Visible input limits
Amounts accept up to 30 digits and 12 decimal places and are capped at 1e12. Annual change is −100% to 1000%; projections use at most 100 years or 1,200 months, and a no-spend challenge at most 3,650 days.
International scope
No currency, tax, inflation rate, wage path, market return, withdrawal rule, price database, or recommended spending standard is assumed.
Projection boundary
Long-range results are deterministic illustrations of entered assumptions, not forecasts, guarantees, financial advice, or value judgments about spending and work.
Calculator-specific assumptions
Use the same period, income convention, and currency for both observations. The calculator measures entered nominal change and does not separate inflation, household-size changes, or deliberate quality changes.