APR stands for "Annual Percentage Rate", or in otherwords, how much interest you pay over a full year. For example, interest at 10% on $100 would be $10 for the year.
At Ideal Lending (and most, but not all other lenders) interest is calculated daily. This means that every day you have your loan you owe a little bit more in interest. You can calculate exactly how much interest using the following formula:
(Principal outstanding × APR) ÷ (365 × number of days)
For example if you have a $500 loan with a 150% APR for 12 days you will owe $24.66 in interest; calculated as follows:
($500 × 1.5) ÷ (365 × 12) = $24.66
With this loan, interest is accruing at $2.05 per day. You should still pay close attention to APR because it is the number that is being used to determine how much interest you are paying every day!
Notice: This is a simple explanation and the specifics may vary with things like effective APR or compounding or other variables.