We need something similar and conspicuous for mortgages. Let people really see/feel the interest.
Another way I’ve seen it phrased is in terms of buying power, and I think that can be effective. I’m ball parking some numbers here, but I think I saw something along the lines of, for the same monthly payment you can buy a $275,000 house with 5% interest or a $350,000 house at 3% interest. I think that drives the point a bit
People who can't (or don't want to) math aren't likely to suddenly do so because of an additional disclosure.
The disclosures you get from the lender are already required to contain a a "FINANCE CHARGE" which is the total interest you will pay on the loan, "The dollar amount the credit will cost you". They also have "TOTAL PAYMENTS", the "The amount you will have paid after you have made all payments as scheduled."
The forms are formatted clearly. If you want to know what the number is, it is right there with an explanation.