Individual & Family Tax
Why Is My Spouse's Income So Low, Yet Our Estimated Tax Payment Is So High?
A CPA Explains One of the Most Common Tax Questions
Topics in this guide:Estimated taxMarried filing jointlySelf-employment tax
Every tax season, I receive the same question from married couples.
"My spouse only earned about $35,000 this year. Why is our estimated tax payment almost $20,000? Is my spouse paying more than 50% in taxes?"
The short answer is:
No.
The estimated tax payment is not based solely on your spouse's income.
Instead, it is calculated using your entire joint tax situation.
Let's look at an example.
Example
Suppose a married couple files a joint tax return.
John
W-2 Salary: $352,168
Mary
Self-employed
Net Business Income: $35,625
After preparing a tax projection, their CPA recommends estimated tax payments of approximately $19,500 for the remainder of the year.
John asks:
"Mary only earned $35,625. Why do we have to pay almost $20,000?"
This is a very reasonable question.
The Answer
The estimated payment is not Mary's tax alone.
It represents the projected tax for the entire household after considering:
- Combined income
- Federal income tax
- California income tax
- Self-employment tax
- W-2 withholding
- Home office deduction
- Other business deductions
- Any remaining balance due
Q&A
Q1. Why doesn't Mary's income start from the 10% tax bracket?
Because John and Mary file Married Filing Jointly.
The IRS combines both incomes into one tax return.
John's salary has already filled the lower tax brackets.
Mary's additional income is added on top of John's income and is generally taxed at the couple's current marginal tax rate.
Q2. What is a marginal tax rate?
A marginal tax rate is simply the tax rate that applies to your next dollar of taxable income.
It does not mean all of your income is taxed at that rate.
The LEGO Tower Explanation
This is the easiest way I have found to explain marginal tax rates.
Imagine building a tower with LEGO blocks.
Each layer represents a tax bracket.
| LEGO Level | Tax Rate |
|---|---|
| Level 1 | 10% |
| Level 2 | 12% |
| Level 3 | 22% |
| Level 4 | 24% |
| Level 5 | 32% |
| Level 6 | 35% |
| Level 7 | 37% |
John's salary has already built the LEGO tower well into the 24% level.
When Mary earns another $35,625, those LEGO blocks don't start from the bottom.
They are simply placed on top of John's existing tower.
Therefore, most of Mary's additional taxable income falls into the current marginal tax brackets:
- Federal: approximately 24%
- California: approximately 9.3%
This is why the tax appears much higher than many people expect.
Q3. Is Mary's entire income taxed at 24%?
No.
Only the additional income falls into the higher marginal tax bracket.
The lower tax brackets have already been used by John's income.
Q4. Why is there self-employment tax?
Mary is self-employed.
Unlike employees, self-employed individuals pay both the employer and employee portions of Social Security and Medicare taxes.
This is called Self-Employment Tax and is separate from federal and state income taxes.
Q5. Why can the estimated tax payment still seem so high?
Because a tax projection looks at your entire household, not one person's income.
Your CPA considers:
- Combined household income
- Self-employment tax
- Federal income tax
- California income tax
- Business deductions
- W-2 withholding
- Estimated tax payments already made
A projection should also include the 0.9% Additional Medicare Tax: for married couples filing jointly, it applies to combined wages and self-employment income above $250,000, and John and Mary's combined wages and self-employment income are well above that threshold. John's employer withholds it only on wages over $200,000 paid by that employer, so the withholding may not cover the full amount.
If the W-2 withholding is not enough to cover the projected total tax liability, estimated tax payments help make up the difference.
Q6. Is Mary really paying over 50% tax?
No.
Many people compare:
- Mary's income: $35,625
- Estimated payment: $19,500
and conclude:
"Mary is paying over 50% in taxes."
That conclusion is incorrect.
The estimated payment is not calculated solely from Mary's income.
It is based on the entire joint tax return, including John's wages, Mary's business income, deductions, withholding, and the couple's projected total tax liability.
Final Thoughts
One spouse's income should never be viewed in isolation.
When a married couple files jointly, every additional dollar earned is added to the household's total taxable income.
Understanding marginal tax rates helps explain why a relatively small increase in income may result in a much larger estimated tax payment than expected.
💡 Kit Leung CPA Tip
Think of your taxes like building a LEGO tower.
The lower tax brackets are the bottom layers.
Once those layers are filled by one spouse's income, the other spouse's income simply adds another LEGO block to the top.
That is how the U.S. marginal tax system works.
The material on this site is general information, not tax advice, and does not create a client relationship. Your situation may differ. Speak to us before you act on anything here.
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Next step
If this applies to you, book an appointment with Kit. A first meeting to start a service is free; advice on your own tax question is a paid consultation.