if a date changes i want cells to be copied elsewhere but only dependent on the date

I have a spreadsheet where I am showing 'current month forecast' and 'last month forecast'. I want to try and automate it so that when another cell (A1, for example) changes date that 'current month forecast' automatically moves into 'last month forecast' and then 'current month forecast' resets to zeros. I have done that as a macro with a simple copy&paste, but I only want that to happen when the date changes, for example below:

DATE / LAST MONTH FORECAST / CURRENT MONTH FORECAST
1-Mar / 3 / 4

DATE / LAST MONTH FORECAST / CURRENT MONTH FORECAST
1-Apr / 4 / 10

DATE / LAST MONTH FORECAST / CURRENT MONTH FORECAST
1-May / 10 / 6