Retaining Row Data

Hi

I have the following spreadsheet which is my sales figures, each day I come home I put the results of the day in columns c and d. As I move to the next day I would like the results of the previous day to remain as they were for that day, trouble is as I input a new days results it’s changing the previous days as well for some of my calculations and I cant figure out how to retain a days results. For instance Need Per Day To Flow on 3 sept is £1320, when I put a days results in 20 Sept, the 3rd sept changes, I want it to stay at £1320 and all results to stay as they were for that day. Could you help? Sept is the first month Ive been doing this and Ive had some holiday, hence the holiday entries but Oct will be a full month, see the tabs at the bottom. Basically Im trying to create a sheet that I can simply put my figs of the day in and the rest calculates itself retaining the actual days results. Any help much appreciated.