No, it does not work that way. Refer back to the tax bucket post. The amount of tax you paid in each bucket under your AGI (actually taxable income, but just forget that detail) never changes as your AGI goes up. Here is the 2014 federal tax brackets for Married Filing Jointly. At $73,800 taxable income your total tax is $10,162.50. If you earned another $1000 to increase your taxable income to $74,800 your tax would go up by $250 to $10,412.50. So your extra $1000 income was taxed at 25% and the tax on your first $73,800 income stays the same.
[TD="colspan: 2"]
2014 Federal Tax Rate Schedules
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[TD="width: 5%"][/TD]
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[TD="width: 16%"][/TD]
[TD="width: 20%"][/TD]
[TD="width: 20%"][/TD]
[TD="width: 22%"][/TD]
[TD="width: 5%"][/TD]
[TD="width: 16%"][/TD]
[TD="width: 16%"][/TD]
[TD="width: 40%, colspan: 2"]
Married Filing Jointly
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[TD="width: 5%"][/TD]
[TD="width: 16%"][/TD]
[TD="width: 16%"][/TD]
[TD="width: 40%, colspan: 2"]
If Taxable Income is:
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[TD="width: 22%"]
The tax is:
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[TD="width: 5%"][/TD]
[TD="width: 16%"][/TD]
[TD="width: 16%"]
of the amount over:
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[TD="width: 20%"]
Over
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[TD="width: 20%"]
Not Over --
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[TD="width: 22%"][/TD]
[TD="width: 5%"][/TD]
[TD="width: 16%"]
Rate
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[TD="width: 16%"][/TD]
[TD="width: 20%"]
-
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[TD="width: 20%"]
18,150
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[TD="width: 22%"]
$ -
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[TD="width: 5%"]
+
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[TD="width: 16%"]
10%
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[TD="width: 16%"]
0
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[TD="width: 20%"]
18,150
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[TD="width: 20%"]
73,800
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[TD="width: 22%"]
$ 1,815.00
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[TD="width: 5%"]
+
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[TD="width: 16%"]
15%
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[TD="width: 16%"]
18,150
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[TD="width: 20%"]
73,800
[/TD]
[TD="width: 20%"]
148,850
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[TD="width: 22%"]
$ 10,162.50
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[TD="width: 5%"]
+
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[TD="width: 16%"]
25%
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[TD="width: 16%"]
73,800
[/TD]
[TD="width: 20%"]
148,850
[/TD]
[TD="width: 20%"]
226,850
[/TD]
[TD="width: 22%"]
$ 28,925.00
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[TD="width: 5%"]
+
[/TD]
[TD="width: 16%"]
28%
[/TD]
[TD="width: 16%"]
148,850
[/TD]
[TD="width: 20%"]
226,850
[/TD]
[TD="width: 20%"]
405,100
[/TD]
[TD="width: 22%"]
$ 50,765.00
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[TD="width: 5%"]
+
[/TD]
[TD="width: 16%"]
33%
[/TD]
[TD="width: 16%"]
226,850
[/TD]
[TD="width: 20%"]
405,100
[/TD]
[TD="width: 20%"]
457,600
[/TD]
[TD="width: 22%"]
$109,587.50
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[TD="width: 5%"]
+
[/TD]
[TD="width: 16%"]
35%
[/TD]
[TD="width: 16%"]
405,100
[/TD]
[TD="width: 20%"]
457,600
[/TD]
[TD="width: 20%"]
-----------
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[TD="width: 22%"]
$127,962.50
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[TD="width: 5%"][/TD]
[TD="width: 16%"]
39.6%
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[TD="width: 16%"]
457,600
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