Impulse Purchase Impact Calculator

This calculator doesn't judge any specific purchase — Weekly Impulse Spending is simply whatever average dollar amount you decide represents your own unplanned or discretionary spending, whether that's takeout coffee, app subscriptions, or online shopping you didn't plan for. The number you enter is the input the entire projection is built from, so the honesty of the result depends entirely on how accurately you've estimated your own weekly discretionary spending.

Current Age only feeds Impact by Age 65, a separate output that compounds your weekly contribution for exactly the number of years between your entered age and 65, rather than the Time Horizon you set elsewhere. Future Value If Invested, Opportunity Cost, and both impulse-cost figures all run on Time Horizon instead, so changing your age alone won't move those numbers — you'd need to change Time Horizon to see a different projection there.

No — Opportunity Cost is specifically the difference between Future Value If Invested and the raw total you contributed (Monthly Impulse Cost times the number of months), meaning it represents only the investment growth you'd be giving up, not the spending itself. Your actual total spending over the Time Horizon is closer to the Annual Impulse Cost multiplied by the number of years, which is a separate and typically much smaller figure than Opportunity Cost once compounding has had years to work.

Very sensitive over long horizons, because Expected Annual Return compounds every single month for the full Time Horizon — a couple of percentage points' difference in the rate can change Future Value If Invested substantially by year 20 or 30, even though it barely matters in year one or two. The default of 8% approximates a long-run historical stock market average, but actual returns vary widely year to year and are never guaranteed, so treat the projection as illustrative rather than a promised outcome.