The effective tax rate is total tax for a period divided by a stated income measure for that same period, expressed as a percentage. It is an average worked out after the fact rather than a rate the law charges, so no statute imposes it and no line on Form 1040 or Form 1120 reports it. The denominator has to be named for the figure to mean anything, because an individual rate is usually struck against taxable income or adjusted gross income while a corporation’s reported rate is struck against pretax book income, and one tax figure gives a different percentage against each.
The Formula, and Why the Base Belongs in the Sentence
effective tax rate = total tax / stated income measure x 100The numerator is total tax, the figure the return itself labels that way: line 24 on Form 1040 and line 31 on Form 1120 (IRS, Form 1040 (2025), IRS, Form 1120 (2025)). Payments never touch it, so withholding and estimated tax change what is owed in April and leave the rate alone. Where that number is read off, and why it is not the balance due, is set out in tax liability.
The two kinds of credit move the rate differently. A nonrefundable credit is subtracted above the total tax line, so it cuts the numerator. A refundable credit sits below it among the payments, so it changes the refund and leaves the rate where it was, and which credits fall on which side is in tax credit.
Total tax on an individual return is also broader than income tax, because line 23 carries other taxes, including self-employment tax, into the line 24 total (IRS, Form 1040 (2025)). A rate struck off that line therefore already includes self-employment tax, while the Social Security and Medicare tax withheld from an employee’s wages never appears among the return’s tax lines and sits outside the ratio entirely. That is why a wage earner’s real burden runs above the rate the return produces, and those charges are set out in payroll tax.
The denominator is a choice. Form 1040 offers three, each no larger than the one above it: total income at line 9, adjusted gross income at line 11a, and taxable income at line 15 (IRS, Form 1040 (2025)). What separates the first two is a closed statutory list, worked through in adjusted gross income. Dividing one total tax figure by three different bases gives three different percentages, all of them arithmetically correct and none of them comparable to each other.
Effective Rate and Marginal Rate Are Not the Same Number
The marginal rate is the rate charged on the next dollar of taxable income. In the individual tables every bracket above the first states the tax as a fixed dollar amount plus a stated percentage of the excess over a threshold, so the percentage attached to a bracket reaches only the slice of taxable income above that threshold, and the highest rate the tables reach is 37 percent (26 U.S.C. 1(j)(2)). Every earlier slice was charged at a lower percentage, so the income tax those tables produce, spread across the whole of taxable income, lands below the rate on the last dollar for anyone whose taxable income runs past the first bracket.
The two rates converge only when the rate never changes. A constant rate makes the average equal the marginal at every level, and the vocabulary for reading rate structures that way sits in proportional tax.
A C corporation is that case on the statute side, since the tax imposed on corporate taxable income is 21 percent of taxable income (26 U.S.C. 11(b)). Its effective rate still moves away from that figure, because credits reduce the tax while the base stays where it was, and because a reported corporate rate is usually struck against book income rather than the taxable income the statute charges.
A Worked Example on One Return
Say a single filer’s 2025 return closes on the figures below, with subtracted amounts in parentheses. Only the base changes across the last three lines. Total tax is taken from line 24, which sits after nonrefundable credits, so it is not the figure the rate tables alone would produce on this taxable income (IRS, Form 1040 (2025)).
Total income (Form 1040, line 9) 100,000
Adjustments to income (line 10) (4,000)
Adjusted gross income (line 11a) 96,000
Deductions (line 14) (15,750)
Taxable income (line 15) 80,250
Total tax (line 24) 11,000
Total tax / taxable income 11,000 / 80,250 13.7%
Total tax / AGI 11,000 / 96,000 11.5%
Total tax / total income 11,000 / 100,000 11.0%One return, one tax figure, three defensible rates. The deduction line is what opens the gap, because the standard deduction on its own puts taxable income well below the figure at the top of the return, so the rate measured against total income is always the flattering one.
Where the Rate Shows Up in a Firm’s Work
The effective tax rate is an output read off a finished return rather than an input to one, which is why it earns its keep only after the numbers are final: comparing a client year to year, testing an entity election, and checking a completed return against the provision booked for the same period.
That last comparison is the one most often misread. Income tax expense over pretax book income is a book rate, built under ASC 740 from current tax plus deferred tax, and a public business entity discloses a rate reconciliation for it on an annual basis (FASB Accounting Standards Update 2023-09, Income Taxes (Topic 740)). The rate off the return is total tax over a stated return measure instead, so the two answer different questions rather than checking each other, and where the gap between them comes from is worked through in the income tax provision.
For a pass-through the entity’s own effective rate says almost nothing, because a partnership is not subject to the income tax as such and an S corporation is only by exception, so the tax lands on the owners’ returns instead. Which entity carries the liability, and the narrow exceptions where an S corporation does pay tax itself, are in federal income tax liability.
Common Questions
How Do You Calculate the Effective Tax Rate?
Divide total tax for the period by the income measure you have named, then multiply by 100. For a C corporation the same division runs total tax at line 31 of Form 1120 over taxable income at line 30 (IRS, Form 1120 (2025)), or income tax expense over pretax book income when the figure wanted is the reported one.
How Do I Calculate My Effective Tax Rate on Form 1040?
Read line 24 for the numerator, then pick the denominator from line 9, line 11a or line 15 and say which one you picked (IRS, Form 1040 (2025)). No line on the form reports the result, so the division happens off the return.
How Do I Calculate My Effective Tax Rate for 2026?
The same division, on a 2026 return. The arithmetic never changes from year to year, while the year’s bracket thresholds, deduction amounts and credits do, so a rate for a year is provisional until that year’s return is complete. Anything computed before then is an estimate of a rate rather than the rate.
What Is the Effective Tax Rate on $100,000?
There is no single answer, because the question names an amount without naming the base, the filing status or the year. An amount of total income is not the same amount of taxable income: the standard deduction for a single filer on a 2025 return is $15,750 on its own (IRS, Form 1040 (2025)), before a single adjustment or credit, and the amounts for the other filing statuses are in standard deduction. Name the base and the year, then divide.
Accountably places trained offshore tax preparers inside US CPA and EA firms, and a firm can put a block of its own return preparation and review work through a trial task before a client file depends on it.
