Again, your post-FIRE income target is not the same as your current monthly income.
Instead, base it on your expected monthly living expenses. Keep in mind that those may or may not resemble your current living expenses. If you plan to live in the same house, and continue living a similar lifestyle, then you can use your current living expenses here.
But don’t fall into the trap of assuming your post-FIRE life will look exactly like your current one. You could move abroad, or to another state or city. If you quit your job, you won’t need to spend money on work clothes or on your daily commute anymore. Your lifestyle might look considerably different.
Plan out your post-financial independence or post-retirement lifestyle carefully, to get a good sense of exactly how much income you’ll need each month. And remember: the less you plan to spend, the less you need to save, and the faster you can reach financial independence! Toy around with the numbers in the FIRE calculator above to see just how much of a difference even $100/month in income has on your target nest egg.