Pro Rata Formula

Hello,

I have data that show the actual sales and the budget for each month. Each line is the data is for the full month, not indivudal days.

I am ususing a gauge chart and I want a target figure of sales pro rata. So total budget divided by 365 to give me a day target. Then take that day target and multiply by the day of the year for example today 31st may is the 151st day of year

Im not sure how to do this, if it shoudl be a measured column or something else?