Why the Overemployed Owe Every April: Fixing Two Paychecks' Withholding Before the Penalty Lands.
Each employer withholds federal tax as if its paycheck is the only one you have, applying the standard deduction and the low brackets twice. Stack two jobs and you are quietly under-withheld at your true marginal rate, which is how a high earner ends up with a five-figure balance due and an underpayment penalty on top.
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