Using a roll-up report to track spend



I am using a large sheet to track contracts that I send out to developers. The contracts are listed with a different budget lines. I am pulling the info from each of these contracts into separate sheets based on their budget line.

I have worked out how to total the value of each of these roll-up reports, but what I actually need to do is total each set of contracts in the roll-up report per month, so I can see our monthly spend. Is this possible?

Thank you!