Calculating rolling sums

[SKB]

I have a year table and enter monthly amounts. I need to calculate the last
three months that have data in the cells. What formula do I use?

 

[Frank Kabel]

Hi
could you provide some more details about your data structure. e.g.
post some example rows.

 

[SKB]

The data is in table form listing work hours and the percentage of time spent
on each catagory permonth.
jan feb mar april may jun july etc. three month total
12 month total
75 84 93 71
I have all of the months in the table, but only want to calculate the last
three months each month. So in the example above, I have data entered for the
first 4 months. I want to calculate the last 3 months and not include the
future months. I also want to calculate ytd. The raw data is
imported/manually entered.