I don't know that there's anything specifically for that on Excel although I suppose someone has created a pretty interface. Essentially what you are looking to do is add current assets (say, a savings and a checking account), then parse them out per month, probably with liabilities (rent, food, etc.) taken out.
Hence something like -
Month Checking Savings Rent Food Difference
January $100 $200 $50 $75 $175
The formula for the difference column would be =B2+C2-D2-E2
and then copy it all the way down the page.
For something more sophisticated, that would take into account interest and the like, you might want to see if your bank has any online tools.