Remember back to your early years in school? You rehearsed this poem?†
"Thirty days hath September,
April, June, and November,
All the rest have thirty-one,
Excepting February alone,
Which has but twenty-eight days clear
And twenty-nine in each leap year.
That poem will come in handy as you calculate the exact number of days for your loan with this strategy.† (It will also work to determine which day of the year you were born on!)