Why is my equation for IF statement inaccurate?

$0.10 fine for overdue of 7 days and below. $0.20 fine for overdue of more than 7 days.

overdueDays = int(input('Enter number of days overdue:'))

def Fines(a = 0.10, b = 0.20):
    if overdueDays <= 7:
     fine1 = a * overdueDays
     print('{:.2f}'.format(fine1))
     return fine1

    else:
     fine2 = b * overdueDays
     print('{:.2f}'.format(fine2))
     return fine2

#Do not remove the next line
Fines(overdueDays)