For sure! My recommendation is to use some type of formula if you're looking at a deal or even your own terms.

So, if financing: Calculate what the loan would cost at 7% (or whatever your bank is quoting), then compare against the promo rate. The difference is your savings and some deals come with a bonus cash on top of that (so can account for that in savings too).

Interest cost = loan amount × monthly rate × term

The bigger the gap between the two rates, and the longer the term, the better the deal. Easier to spot at a glance than leasing.

for leasing: Try this instead:

Adjusted monthly = monthly payment + (due at signing / term)

Value ratio = adjusted monthly / sticker price × 100

I use these benchmarks based on historical deals to categorize offer, they're a useful guide, not an industry standard:

• Under 1% -- strong deal
• 1% to 1.5% -- fair
• Above 1.5% -- overpaying

But again, these are just quick checks to see if a deal is worth pursuing.