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Does my net paycheck decrease as the year goes on due to tax brackets filling up?
In general no, if you just have one employer and work there with the same salary for the whole year.  Typically an employer does tax withholding by extrapolating your monthly income to the entire year and withholding the right amount so that at the end, what is withheld is what you owe.  It's not a surprise to them when your income crosses a tax bracket threshold, because they knew how much they were paying you and knew when you would cross into another bracket, so they factored that in. If you have multiple jobs or only worked for part of the year, or if your income varied from month to month (e.g., you got a raise) there could be a discrepancy between what is withheld and what you owe, because each employer only knows about what it's paying you, not what money you may have earned from other sources.  (Even here, though, the discrepancy wouldn't be due to the tax brackets per se.)  You can adjust your withholdings on form W-4 if needed, to tell the employer to withhold more or less than they otherwise would.