I do this all of the time. And it involves no math (that I have to do, anyway).

First of all, the day before (or sooner), I have my recipe in the brewing software. I make sure everything looks good (the pre-boil gravity, the post-boil gravity, volumes, etc).

After sparging, I take a pre-boil gravity and volume. If I'm a little low on gravity and a little high on volume, If I'm ok on volume and low enough on gravity, I run downstairs and open the recipe in the brewing software. I change the mash efficiency (or something) to make the receipe look like what I ended-up getting for my gravity. I then add DME to the recipe in various amounts (trial and error) until I get back to the target pre-boil gravity. And a positive side-effect is that now your recipe software is more in line with your equipment.

I do this all of the time. And it involves no math (that I have to do, anyway).

First of all, the day before (or sooner), I have my recipe in the brewing software. I make sure everything looks good (the pre-boil gravity, the post-boil gravity, volumes, etc).

After sparging, I take a pre-boil gravity and volume. If I'm ok on volume and low enough on gravity, I run downstairs and open the recipe in the brewing software. I change the mash efficiency (or something) to make the receipe look like what I ended-up getting for my gravity. I then add DME to the recipe in various amounts (trial and error) until I get back to the target pre-boil gravity. And a positive side-effect is that now your recipe software is more in line with your equipment.