I have a P&L by month on a "Monthly" tab. It has the last 3 years or 36
months of data.

I need to create a "Quarterly" tab where I sum the months into quarters.

So my monthly tab has data in column A through AJ.

I need the first Quarterly column to sum columns A:C from the Monthly. Then
I want the second column to sum columns D:F from the Monthly. The problem is
that if I drag the formulas like normal the second Quarterly column will add
B:D from the Monthly since it is looking relative.

Is there a way to tell it how many columns to skip when copying the formulas
over? This could even apply to summing monthly data into annual data.

Thanks!