 # Conditional Roll Up within a Table

Hi there,

I would love to get some guidance on how to do something like a conditional roll up within one table.

If you see the table example below you can see that I have contractual start and end dates that I want to use as a guide for calculating Total Revenue so that I can calculate % of monthly revenue against the total revenue.

It is the TOTAL REVENUE column that I am having difficulty with as I don’t know how to make the calculation conditionally based on the contractual year that a particular month falls within. And as you can see, a contractual year may differ from calendar to financial year.

Is there a way to do this?

I would use a linked table to assist with the calculations. Make a table called `[Contractual Years]`. The primary field would be a formula to concatenate two other fields where you specify the start and end month-year combo for a given contractual year: In your primary table, you would link to a specific contractual year for each month. On the `[Contractual Years]` table, you would add a rollup field that would tally all of the monthly revenue values for linked months.

Back in your main table, you would add a lookup field to pull in this total. A `{Percent of Total}` formula field would do the math to determine how much each month factored into the total.

``````IF({Total for Contractual Period}, {Monthly Revenue} / {Total for Contractual Period})
``````

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