Wrong. The person only needs to know how much his income was for the prior year and that will usually be how much he has spent (for most people). Removing any savings (if he has them) would be a no-brainer since it would not be spent.
Multiplying 23% times his expenditures would give him a very good approximation of what it will "cost" him. The thing not seen in this, though (or by you either) is the extra amount he will pay in the form of hidden taxes which are increases in the prices of things caused by the income tax. This increase will be REMOVED from prices, making the things he buys under the FairTax less expensive before being the tax is applied. In addition to the lowered prices, he will have his full paycheck under the FairTax (plus the prebate) since taxes will no longer be withheld by the employer.
So you see, there are several things that need to be considered other than just simply looking at the single rate number.
And calculations using t.e. of 30% is wrong as you've presented it since based upon the t.i. of 23% currently in the bill, that would make the t.e. 29,87% rather than 30%.
Ah, all becomes clear now. You're still in college, and haven't had to support yourself yet. Now that that's clear, I apologize for trying to discuss this with you; it's only natural that you don't know how the world actually works.
Removing any savings (if he has them) would be a no-brainer since it would not be spent.
I can confidently subtract church tithes, and I think I can remember what my 401(k) contribution is. Of course there's the direct deposit to savings, some of which is automatically transferred to the money market account... yup, subtracting my savings is a snap. Since I use Quicken, I could of course figure it out in about 20 minutes after I get home.
But what about expenditures on used items? You're simply blathering--but as I said, it makes perfect sense given that you've never actually had to manage a real household budget.