Yes, these are reasons why practical math and financial literacy are important subjects to be taught.The worst I've ever heard was an hourly employee who was turning down overtime because "if you make too much money, you get bumped to the next tax bracket actually take home less." It is amazing how many people don't understand how tax brackets or withholdings work.
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"Usually" is correct because it depends on rate. Our latest purchase offered a 0% rate or $500 cash back. Less than a 1% return if we took the cash back so we'll let that loan ride.
I find a lot of people are debt adverse without really considering that there is math involved.
I can't even count how many times I've heard the same thing about tax brackets or a complete lack of understanding about how a tax refund works.
When I went with my daughter to buy a car there was an offer for a 0% interest loan that had a $750 fee. I did a quick amortization calculator and the total interest that would be paid over the life of a 3% interest loan was less than $500. So, it would actually have been MORE expensive to take the 0% loan than the 3%, but I think the vast majority of people would have just automatically taken the 0% loan because it seems like it would be less. I mentioned it to the finance manager and he just said, "Yeah, most people don't do math"