Lesson 2 of 7
How Withholding Works
Anthony filled out a W-4 when he started at Amazon five years ago. He answered the questions, handed it to HR, and never thought about it again.
That W-4 has been running his tax withholding ever since. Through two raises. Through a bonus. Through the year he picked up Uber on weekends.
And nobody told him to update it.
That’s how most people end up with a tax surprise in April.
Withholding is how most people pre-pay their taxes throughout the year. Instead of writing the IRS one giant check in April, your employer takes a little out of every paycheck and sends it to the IRS on your behalf. By the time April comes, you’ve already paid most or all of what you owe.
The question is whether the amount coming out each paycheck is right for your actual situation. And that’s controlled by one form most people fill out once and forget about forever.
💬 Words You'll Hear in the Office
W-4Employee’s Withholding Certificate — the form you fill out at work that tells your employer how much tax to take from each paycheck
WithholdingThe money your employer pulls from your paycheck and sends to the IRS before you ever see it
Under-WithholdingWhen not enough tax comes out during the year — leads to a balance due in April
Over-WithholdingWhen too much tax comes out — leads to a refund in April but means the IRS held your money all year
FICAFederal Insurance Contributions Act — the payroll tax for Social Security and Medicare, 7.65% from you every paycheck
What the W-4 Actually Does
The W-4 is a simple form. You fill it out, give it to your employer, and they use it to figure out how much federal income tax to pull from each paycheck. It asks about your filing status, whether you have other jobs, and whether you want extra money withheld.
Here’s the problem: the W-4 only knows about the income from that one job. Amazon sees Anthony’s Amazon income. That’s it. When Anthony started driving Uber on weekends and making an extra $11,000 a year, Amazon had no idea. The W-4 Anthony filled out in 2019 was still running. Still withholding for a single-income situation. Still sending the same amount to the IRS every week.
The Uber income came in with zero withholding. Zero. By April, Anthony owed tax on $11,000 that nobody had collected throughout the year. That’s the gap.
The Two-Job Problem
This trips up a lot of people. When someone works two jobs, each employer withholds as if that’s the only income. But tax brackets are based on total income. If the combined income is higher than what either employer accounted for, the total withholding might not be enough — even if both employers did their jobs correctly.
💵 Anthony’s Withholding Problem
Amazon income — withheld correctly for this job$38,000 / $3,800 withheld
Uber income — zero withholding all year$11,000 / $0 withheld
Combined income the IRS taxes him on$49,000
Tax owed on $49,000$5,600
Total withheld throughout the year− $3,800
Balance due — the gap nobody filled$1,800
The Fix — It’s Simple
There are two ways to solve under-withholding:
Update the W-4. On the W-4, there’s a line for additional withholding — an extra dollar amount you want taken out of each paycheck. If Anthony adds $75 per paycheck in extra withholding at Amazon, that’s roughly $1,950 extra going to the IRS over 26 paychecks. The Uber gap is covered. No April surprise.
Make quarterly estimated payments. Instead of changing the W-4, pay the IRS directly four times a year on the gig income. We cover this in Lesson 4. Either approach works — the right one depends on the client’s situation.
💬 Fixing Anthony’s W-4
🚫
Anthony
So my W-4 is messed up?
RM
Ralph
It’s not messed up — it just hasn’t been updated for your actual situation. When you started at Amazon you had one income. Now you have two. The W-4 still thinks you have one.
RM
Ralph
Easy. On your W-4, there’s a spot for extra withholding per paycheck. Based on your Uber income, I’d put about $75 extra per paycheck. Over the year that covers the gap. Next April you break even instead of owing.
🚫
Anthony
And that doesn’t mean I’m paying more tax overall?
RM
Ralph
Right. Same total tax. You’re just spreading the payment through the year instead of hitting it all in April.
🏢
Real Office Scenario
A new client comes in. She has a W-2 from a hospital where she works as a nurse. She also did some contract work on the side for a staffing agency and got a 1099-NEC for $14,000. She made no estimated payments. You run the return and she owes $3,100. She’s shocked. She thought the hospital withholding covered everything.
It did — for the hospital income. The 1099 income had zero withholding. The fix going forward: either add extra withholding to her hospital W-4, or make quarterly estimated payments on the contract income. She doesn’t need to pay more tax. She just needs to pay it on time.
⚠️
Common Beginner Mistake
Not asking about all income sources before reviewing withholding. If a client has a W-2 and you only look at the W-2 withholding, you might think they’re fine. But if they also have gig income, rental income, or a side business, the W-2 withholding is only covering part of the picture. Always ask: “Any other income this year beyond this W-2?”
🕐
Slow Down & Ask Questions
When a client says they “have withholding” — slow down. Ask which job. Ask how much. Ask if they have any income where nothing was withheld. Withholding from one job does not cover income from other sources.
📋 From the Desk of Ralph Martinez
I update W-4s for clients all the time. It takes two minutes and it saves them from a surprise in April. If someone comes in owing money and they’re not self-employed — the first thing I look at is their W-4. Nine times out of ten, it’s outdated.
— Ralph Martinez · Ruskin, FL · Est. 2001