@NCperson - You're right. I think in all regards.
For the 600,000 example I scrapped my manual calc spreadsheet already, but I am going to assume you are correct as that was a hasty test increasing the numbers and I very well may have used the wrong table between my two data sets as I was switching back and forth.
I started seeing this problem as I was working on an Excel spreadsheet to manually calculate taxes using the brackets. TBH, most of what I know about taxes is from using TurboTax for 10 years and sometimes working backwards from filling out the questions and then manually reviewing each form. I'll admit, I was confused/ignorant about the "Tax Table." I had assumed that the Tax Table meant simply using the bracket incomes to calculate (similar to your graph and what I was working with in Excel). I never realized there was an actual document that provided a table to lookup tax owed like the yellow pages! I assume this is meant to make it easier for people doing taxes by hand to find out the tax rather than computing via a "graph table" like you show.
Since the "tax tables" provide a broader range, it looks like the taxed owed is rounded up a bit (or I guess down depending on your scenario), and that accounts for the small discrepancy in amount.
I guess I should have put more trust in TurboTax here, seeing as I do let them do my taxes every year 🙂
What is surprising is that the other links I mention are doing it wrong! TaxAct and HR block estimators.
In their defense, those are "estimators" and their actual products may compute correctly, but it appears their backend is built to use the brackets, whereas the online Intuit Taxcaster is actually properly doing a lookup against the "Tax Tables."
Thanks for teaching me something new.
