adjustments to PHP+MySQL application

We have a statistics program built in-house (simple php + mySQL) that records sales for day/week/month/year. currently we can edit goals on daily, weekly monthly, and yearly. we only want to be able to edit the monthly. and then have the monthly goal divide or multiply to create the daily, weekly, and yearly. the reason for this is because the daily goal should change based on actual vs. projected. So let's say monthly goal is 10,000 -- the daily goal would be 333. if day one of the month comes and goes and makes 200 in sales, the daily goal would then increase to accommodate the total monthly goal if monthly goal is 30,000 and we are 7 days into the 30-day month with 12,000 in total sales to date... it would be 30,000 - 12,000 = 18,000 / 23 = ~782 per day. 782 * 23 = 18,000 + 12,000 = 30,000. at beginning of the month it would be 1,000 per day, on day 7 it would be 782 per day. Please let me know if I can clarify additional. So to clarify, we want to have our goal editable on the monthly part only and have that monthly goal used as the basis for daily, weekly, and yearly. The program is 100% php MySQL and Javascript.