Put a number on the purchases you wish you hadn't made.

Most people have a rough sense of how often they regret a purchase. A new shirt that never gets worn. An Amazon order that felt great for an evening and pointless by next weekend. This calculator puts a number on the habit: how much money goes into purchases that, in hindsight, shouldn't have happened.

The arithmetic is simple. If you make 6 impulse purchases a month at 25 each, that's 150 a month. If 50% of them turn out to be regretted, 75 a month is effectively wasted. Over 20 years, that's 18,000 in direct cost - or around 39,000 if the regretted amount had been invested at 7%.

The purpose isn't to shame every purchase. It's to make a feel-based pattern visible. Once the monthly number is concrete, the 24-hour rule (wait a day before buying anything non-essential) or a weekly impulse budget becomes easier to stick to, because the savings are quantified rather than abstract.

Quick example

With impulse purchases per month of 6 and average purchase amount of 25 (plus percentage regretted of 50% and investment return of 7%), the result is 18,000.00. Change any figure and watch the output shift — it's often more useful to see the pattern than to memorise the formula.

Which inputs matter most

You enter Impulse Purchases per Month, Average Purchase Amount, Percentage Regretted, Investment Return (if saved), and Time Horizon. Not every input has equal weight. Flip one at a time toward extreme values to feel which ones move the needle most for your situation.

What's happening under the hood

Monthly regret amount = purchases × average × regret%. Annualised to 12 months and scaled to years. Parallel future-value calculation on the monthly regret amount as a saved alternative. The formula is listed in full below. If the number looks off, you can retrace the calculation by hand — that's the point of showing the working.

Using this as a conversation starter

If the number is shared among household members, it's often easier to discuss than specific purchases. The calculation is neutral; it has no opinion about what's right. That neutrality is useful when conversations might otherwise get tense.

What this doesn't capture

Behaviour-adjacent math is always an approximation. Human habits are lumpy and context-dependent; the figure here assumes steady behaviour which is a simplification. Treat the output as a prompt for thinking rather than a precise prediction.