For a $10,000 loan with 6.80% fixed interest during a non leap year.
Principal balance x interest rate / number of days in this year = daily outstanding interest
$10,000 x 0.068 / 365 = $1.8630
You would accrue $1.863 in interest every day as long as your principal balance is $10,000. If there were 30 days from your last payment and all previous outstanding interest was paid with your last payment, the monthly interest in this example would be $55.89.