Trending forecast in a month

Hello,

I am wondering if there is a way to find the trend of spent vs forecasted.

what I've been asked was to get the trending spent against the forecast as in, the first 20 days we've spent $2000, so over 30 days it should be $3000 (found by dividing total spent against number of days so far in the month then multiplying by total amount of days in month)

is there a way to have the excel spreadsheet do this calculation for me every day? or am I just stuck doing this manually every day?

thanks in advance.