Relative Conversion Rate

Hello again everyone!

I found myself in a persiting doubt and I want to know if someone has faced it before.

My questions is: How can I calculate the converted leads that occured in the same month?

I want to calculate a 'Relative" conversion rate, in a especific cenario and I will try to picture it out:

I have some leads ocurring in month 4, by their ID's. Some of them, converted in the same month. The rest of them, in the next month.

I need to know the convertion rate of all leads ocurring in the same month.

Is there any way to mark them if they converted or not in the same month?

I know its a bit fuzzy but I really hope that could be understood.

Thanks!