Recent promotion and qualifying for a mortgage?

I will be receiving a promotion July 30th of this year. The promotion will occur in the middle of a pay period for me. I am not sure about what official paperwork I will receive. I will have to wait over a month to have two full checks that reflect my new salary (which is 20% higher than my current salary). Do I have to wait to have two full pay checks with my new salary before I can qualify for a mortgage based off of the new salary? I am applying for a conventional mortgage. I plan to get prequalified in August and would like to begin house hunting.

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