How to Calculate S Corp Taxable Income: K Items, Basis, and QBI

To calculate S corp taxable income, you work through Form 1120-S to arrive at ordinary business income (gross receipts minus cost of goods sold minus deductible operating expenses), pull out any items that must be reported separately on Schedule K, and then allocate everything to shareholders by ownership percentage. The S corporation itself usually pays no federal income tax; the numbers you calculate flow to each shareholder’s Schedule K-1 and onto their personal return.¹

Records You Need Before You Start

The calculation only works if the underlying books are complete. Pull a profit and loss statement covering the full tax year and a year-end balance sheet. If the business carries inventory, you need beginning and ending counts plus records of purchases made during the year, because those numbers feed the cost of goods sold line.

Payroll records matter more than people expect. Wages paid to shareholder-employees are deducted as a business expense before anything passes through, so W-2s issued by the company need to reconcile with the salaries and wages line on the return. If the corporation paid health insurance premiums for any shareholder who owns more than 2 percent of the stock, those premiums must have been included in Box 1 of that shareholder’s W-2. The IRS treats them as wages subject to income tax withholding but not FICA, and the shareholder then takes an above-the-line deduction on the personal return.²

You also need the legal business name as it appears in the corporate charter, the physical address, the nine-digit EIN, and the date of incorporation. The effective date of the S election on your return should match what was filed on Form 2553.³

Ordinary Business Income, Line by Line

The main calculation lives on page one of Form 1120-S. Start with gross receipts or sales on line 1a. Subtract cost of goods sold (line 2) to get gross profit.⁴

From gross profit, subtract ordinary and necessary business expenses. Federal tax law allows a deduction for expenses that are both common in your industry and helpful to running the business.⁵ The main categories on Form 1120-S:

Salaries and wages paid to employees, including shareholder-employees
Rent paid for business property the company does not own
Interest on business loans (line 13)
Taxes and licenses, including state and local taxes, payroll taxes, and business license fees
Depreciation, calculated on Form 4562 and carried to line 14
Employer contributions to pension or profit-sharing plans (line 17)
Insurance premiums, office supplies, advertising, and similar costs on line 20

Business meals are 50 percent deductible when a business purpose exists and the meal is not lavish. Entertainment expenses are not deductible at all. Total the applicable deductions and subtract them from gross profit. The result is ordinary business income or loss. A negative number is an operating loss that shareholders may be able to use against other income on their personal returns, subject to the basis rules covered below.

Separately Stated Items on Schedule K

Some items skip the ordinary income calculation and appear on Schedule K instead, because their tax treatment depends on the individual shareholder’s situation. The character of each item stays intact as it passes through, so a capital gain at the corporate level is still a capital gain on the shareholder’s return.¹

Capital gains and losses from selling business assets held as investments
Interest and dividend income from business accounts or corporate investments
Charitable contributions the corporation made, which shareholders claim as itemized deductions
Section 179 deductions for qualifying equipment purchases, up to $2,500,000 for tax year 2025 (adjusted annually for inflation)⁶
Foreign taxes paid, so shareholders can claim the foreign tax credit

Each item is totaled on Schedule K and then allocated to shareholders by ownership percentage on their K-1s.

Paying Yourself: Reasonable Compensation

If you work in the business and own stock, you have to pay yourself a reasonable salary before taking profit distributions. This is one of the most heavily scrutinized areas of S corporation taxation. Wages you receive are subject to Social Security and Medicare taxes; profit distributions that pass through to you are not. That gap is exactly what the IRS watches for.⁷

There is no fixed formula. Courts have looked at training and experience, the time you devote to the business, what comparable businesses pay for similar work, your responsibilities within the company, and the corporation’s dividend history.⁷ If the IRS decides the salary was unreasonably low, it can reclassify distributions as wages and assess back employment taxes plus penalties and interest.

Compensation directly shapes the taxable income calculation. Your salary is a deductible business expense on page one, so it reduces ordinary business income. Whatever profit is left passes through as a distribution. Set the salary too low and you inflate the pass-through and invite audit attention. Set it too high and you pay more payroll tax than you need to.

Allocating to Shareholders and Basis Limits

After the corporation’s ordinary income and separately stated items are set, they are allocated to each shareholder based on ownership percentage and reported on Schedule K-1. Each shareholder must receive a K-1, and the corporation files a copy directly with the IRS.⁸ Shareholders transfer the K-1 figures to Form 1040, typically on Schedule E.

How much of the allocation a shareholder can actually deduct or receive tax-free depends on basis. Basis starts with what you paid for your stock or contributed as capital, then adjusts each year, in this order, as of the last day of the corporation’s tax year:⁹

Increased by your share of ordinary income, separately stated income items, and tax-exempt income
Decreased by distributions you receive
Decreased by nondeductible expenses, such as meals beyond the 50 percent limit
Decreased by your share of ordinary losses and separately stated loss or deduction items

Basis cannot drop below zero. If your share of losses exceeds the combined basis of your stock and any money the corporation owes you personally, the excess is disallowed for that year. The disallowed amount carries forward indefinitely and can be used when basis is high enough to absorb it.¹

Distributions follow a similar rule. If the S corporation has no accumulated earnings and profits from a prior period as a C corporation, distributions are tax-free up to your stock basis. Any amount above basis is taxed as a capital gain, and it is long-term if you have held the stock more than a year.¹⁰ Only stock basis counts for the distribution calculation; debt basis does not.⁹

When the Corporation Itself Owes Tax

Two situations put a tax at the entity level. If the S corporation was previously a C corporation and holds assets that had built-in gains at the time of conversion, selling those assets within the recognition period can trigger a built-in gains tax. And if the corporation has accumulated earnings and profits from a C corporation period and more than 25 percent of its gross receipts come from passive investment income (such as rents, royalties, or interest), a tax applies to the excess net passive income.¹¹

If your S corporation has always been an S corporation with no C history, neither tax typically applies.

The QBI Deduction at the Shareholder Level

S corporation shareholders may qualify for a 20 percent deduction on their share of qualified business income under Section 199A. It is claimed on the personal return, not on Form 1120-S, but the corporate numbers directly feed it. The One Big Beautiful Bill Act, signed in July 2025, made this deduction permanent.¹²

Below certain taxable income thresholds, the deduction is straightforward. For 2025, those thresholds are $197,300 for single filers and $394,600 for married couples filing jointly, adjusted annually for inflation.¹³ Above them, the deduction may be limited based on W-2 wages the S corporation pays and the value of its qualified property.

Certain professional service businesses face additional restrictions. Health care, law, accounting, consulting, financial services, and athletics are excluded entirely once taxable income exceeds the upper end of the phase-in range: $247,300 for single filers and $494,600 for joint filers in 2025.¹³ Because the W-2 wage figure the corporation reports drives the shareholder-level limit, accuracy on Form 1120-S has consequences beyond the corporate return itself.

1
Office of the Law Revision Counsel. 26 USC 1366 – Pass-Thru of Items to Shareholders
2
Internal Revenue Service. S Corporation Compensation and Medical Insurance Issues
3
Internal Revenue Service. Form 2553 – Election by a Small Business Corporation
4
Internal Revenue Service. Instructions for Form 1120-S (2025)
5
Office of the Law Revision Counsel. 26 USC 162 – Trade or Business Expenses
6
Internal Revenue Service. Instructions for Form 4562 – Depreciation and Amortization
7
Internal Revenue Service. Wage Compensation for S Corporation Officers
8
Internal Revenue Service. Shareholder’s Instructions for Schedule K-1 (Form 1120-S)
9
Internal Revenue Service. S Corporation Stock and Debt Basis
10
Office of the Law Revision Counsel. 26 USC 1368 – Distributions
11
Office of the Law Revision Counsel. 26 USC 1375 – Tax Imposed When Passive Investment Income of Corporation Having Accumulated Earnings and Profits Exceeds 25 Percent of Gross Receipts
12
Internal Revenue Service. Qualified Business Income Deduction
13
Internal Revenue Service. Instructions for Form 8995