Impulse spending is any purchase made without prior intention — the item wasn't planned, the decision was made in the moment, and the trigger was environmental or emotional rather than rational. Research consistently shows that people underestimate their impulse spending by 40–60%, evaluating each transaction in isolation rather than recognizing the cumulative pattern. A $35 unplanned clothing purchase, a $22 gadget add-on, a $19 streaming service that felt free at checkout: none triggers a significant response individually. Together, they can represent $200–500/month in spending that delivers variable value and consistent financial cost. The real cost of impulse spending is not the monthly total — it is the compound opportunity cost. Every dollar spent impulsively is a dollar not invested. At 7% annual return, $200/month in impulse spending is $34,000 over 10 years and $104,000 over 20 years. The calculator breaks this down by category — online shopping, clothing, food, tech, home items, entertainment, personal care — and adds a regret percentage that separates impulse purchases you enjoy from those you wish you hadn't made. The goal is not eliminating all unplanned spending. Spontaneous purchases can bring genuine enjoyment. The goal is making the pattern visible: which categories are you impulse-buying most, which do you most regret, and what is the compounding cost of each one? With that picture, you can make deliberate choices rather than continuing a habitual pattern.