I popped onto the tool to mess around but there's nothing to count for inflation! This makes the tool rather convoluted.

I think this is the first time in history that *not* adding inflation makes something convoluted. :)

As much as I'd like to ignore inflation, I can't in the case of this calculator. If I assume only real returns in this case, then as my costs rise over time with inflation, the number I need to save will change, so I'm chasing a moving target. My FI date will be later than the calculator predicts.

This calculator is flawed. I can work with a calculator like

this one, as I'm dealing only in today's dollars. The problem with the Mad Fientist calculator is it attempts to deal with future dollars in returns yet today's dollars in expenses (due to expenses naturally wanting to rise with inflation), which can only result in a flawed prediction. Fine for tracking your monthly progress, but the FI date prediction won't work.

For what its worth, I think inflation in the laboratory is sort of assumed when you set your growth rate under "assumptions". For instance, I set mine to 7%- which if I've understood correctly is based on average total return minus inflation.

The problem with this is that your expenses (and hopefully savings) will rise over time (with inflation), and yet you are assuming your expenses to be fixed at one point in time. The only way to counter this within the limits of the calculator is to multiply your expenses (and savings) by the reduced value of that dollar compared to your first month's starting point.