Rule of 78

The “Rule of 78” is kind of like numerology for loan payments. It’s a way for lenders to front-load interest on a loan so they’ll still make a buck, even if the borrower pays off the loan early.

But before we get into the nitty-gritty details here, let’s just go ahead answer the question on everyone’s mind: why is it called the “Rule of 78?” Well, let’s start with the fact that there are 12 months in a calendar year. Throw some simple arithmetic into the mix, and…

1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 = 78

Okay, now let’s say Beatrice just took out a 12-month loan for $10,000 with a 15% fixed interest rate. Her lender calculates the total interest charge for the loan: $1,500. Then he divides that amount by twelve ($125) and adds that to Beatrice’s monthly payment. This means she’s got twelve equal payments of $958.33 ($833.33 for the loan amount plus $125 for the interest).

Now here’s where stuff gets fun…and a little more complicated. Let’s divide the total interest for the loan by 78, which gives us $19.23. During the first month, when Beatrice has twelve months left on the loan, the payment amount will be divvied up so that 12/78 of the total interest amount will go to the lender, while the rest will go toward the principal. That’s $230.76 in interest and $727.57 toward the principal, for those keeping track. During the second month, when she’s got eleven months left on the loan, 11/78 of the total interest amount will go toward paying off the loan’s interest, which means $211.53 in interest and $746.80 toward the principal. Every month, more of Beatrice’s payment goes toward the loan principal, and less goes to interest.

If she takes the full twelve months to pay back the loan, this really doesn’t matter. But if she decides to pay off the loan early, like in six months, the lender still benefits, because those first few payments are so interest-heavy. Think of it this way: if she paid $125 in interest every month for six months before paying the loan off in full, she’d end up paying a total of $750 in interest. Under the front-loaded Rule of 78, she’d end up paying $1,096.11 in interest.

If this sounds a little unfair, federal legislators tend to agree, which is why the Rule of 78 is illegal on loans that are for longer than 61 months.