Lifestyle Inflation Detector

The calculator subtracts your expense growth percentage from your income growth percentage, so a negative result means your income grew faster than your expenses — you're keeping a larger share of each new dollar rather than spending it away. A positive rate is the warning sign: it means expenses outpaced income, which is the definition of lifestyle inflation this tool is built to detect.

The wealth impact calculation only runs when monthlyExtraSaved (currentExpenses minus previousExpenses) is greater than zero — if your expenses actually decreased between the two periods, that difference is negative and the loop that compounds it monthly never executes, leaving wealthImpact10yr at 0. In other words, this output specifically measures the growth you'd have gained by investing the expense increase instead of spending it; it isn't designed to show a benefit for having cut spending.

Lifestyle inflation rate only compares the relative growth rates of income and expenses, while previousSavingsRate and currentSavingsRate divide your actual savings dollars by your income in each period to show the real share of income you're setting aside. It's possible for income to grow faster than expenses (a negative lifestyle inflation rate) while your savings rate still falls, if your reported savings amount didn't keep pace — tracking both numbers catches that gap.

It's a simplified stand-in for a long-run average stock market return, applied to the monthly expense increase as if that exact dollar amount had instead been invested every month for 120 months, compounding at 8%/12 per month. It ignores taxes, fees, market volatility, and the fact your expense difference might not stay constant every month, so the resulting number is meant to illustrate the scale of the opportunity cost, not to forecast an actual account balance.