Yeah, you have been ripping yourself off! In my area everyone charges by the day, not by the month, so this will never happen. I have some parents who pay monthly and I just add up the number of days in each month and then multiply it by my daily rate and that is what they pay...so it varies month to month. If you want to have a monthly rate that is the same every month, you will have to add up the whole year (52 weeks multiplied by your weekly rate) and then divide it by 12 to get the monthly amount.