I take monthly payment and base my fee on 22 days per month. Some months are 21, some are 23, but I think 20 is really short changing yourself. My rate is flat fee regardless and I take stats off with pay. I reimburse parents the following month in case of having to close due to illness or whatever. I have also started requiring that parents pay a full month deposit which is applied to the last month of care if 1 month notice is given. It's too easy to get totally shafted without that month of deposit with monthly payment. I know from experience!