To pay short-term capital gains tax, calculate the gain at your ordinary income tax rate, report each sale on Form 8949 and summarize it on Schedule D, and send the money to the IRS either through quarterly estimated payments during the year or with your Form 1040 by April 15. The IRS does not run a separate portal for capital gains; the tax rides along with the rest of your income tax, and the practical work is getting the amount right and the payment in on time.
Because short-term gains are taxed as ordinary income, the rate can land anywhere from 10% to 37% for 2026 depending on your total taxable income, and higher earners may owe an additional 3.8% Net Investment Income Tax on top of that.1Internal Revenue Service. Topic No. 409, Capital Gains and Losses
Figure Out What You Owe
A short-term capital gain is profit on a capital asset you held for one year or less, including stocks, bonds, mutual fund shares, and digital assets.2Office of the Law Revision Counsel. 26 USC 1222 – Other Terms Relating to Capital Gains and Losses Unlike long-term gains, short-term gains get no preferential rate. They stack on top of your wages and other income to determine which bracket applies.1Internal Revenue Service. Topic No. 409, Capital Gains and Losses
Before applying that rate, net your gains against your capital losses for the year. Short-term losses offset short-term gains first, and long-term losses offset long-term gains first; any remaining loss in one category then offsets gains in the other. If losses exceed gains overall, you can deduct up to $3,000 of the net loss against ordinary income ($1,500 if married filing separately), with the rest carrying forward indefinitely.3Office of the Law Revision Counsel. 26 USC 1211 – Limitation on Capital Losses
For 2026, the ordinary rate brackets a single filer will hit range from 10% on income up to $12,400 to 37% on income over $640,600, with the standard deduction at $16,100 for single filers, $32,200 for married filing jointly, and $24,150 for head of household.4Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026 Only the portion of income within each bracket is taxed at that bracket’s rate, so a gain that pushes you across a bracket line means only the overflow is taxed at the higher rate.
The 3.8% Net Investment Income Tax
If your modified adjusted gross income exceeds $200,000 (single or head of household), $250,000 (married filing jointly), or $125,000 (married filing separately), you owe an extra 3.8% on the lesser of your net investment income or the amount over the threshold.5Internal Revenue Service. Net Investment Income Tax Short-term gains count as net investment income. These thresholds are set by statute and are not indexed for inflation.6Office of the Law Revision Counsel. 26 USC 1411 – Imposition of Tax Combined with the top ordinary rate, the surtax raises the top federal rate on short-term gains to 40.8%.
When You Have to Pay
If you expect to owe $1,000 or more after subtracting withholding and refundable credits, the IRS generally requires estimated payments during the year rather than a single check in April.7Internal Revenue Service. Form 1040-ES, Estimated Tax for Individuals This is where a lot of investors slip up: a big gain in March or July doesn’t wait until April of the following year to be paid.
The 2026 quarterly due dates are April 15, 2026; June 15, 2026; September 15, 2026; and January 15, 2027. You can skip the January payment if you file your 2026 return and pay the full balance by February 1, 2027.7Internal Revenue Service. Form 1040-ES, Estimated Tax for Individuals
Safe Harbor: How Much to Send
You avoid an underpayment penalty if your estimated payments plus withholding cover the lesser of 90% of your 2026 tax liability or 100% of the tax shown on your 2025 return. If your 2025 adjusted gross income was over $150,000 ($75,000 if married filing separately), the prior-year figure jumps to 110% of last year’s tax.8Office of the Law Revision Counsel. 26 USC 6654 – Failure by Individual to Pay Estimated Income Tax Investors coming off a strong prior year often miss the 110% step-up and get a penalty they weren’t expecting.
If your gains bunched into one part of the year, the annualized income installment method lets you base each quarter’s payment on income actually earned by that point, calculated on Schedule AI of Form 2210.9Internal Revenue Service. Form 2210, Underpayment of Estimated Tax by Individuals, Estates, and Trusts
How to Send the Payment
Once you know the amount, the IRS accepts payment several ways. Use the same methods for a quarterly estimated payment and for the balance due with your return; only the accompanying voucher differs.
IRS Direct Pay. Free, no registration, pulls funds directly from your bank account, and gives you an immediate confirmation number.10Internal Revenue Service. Pay Personal Taxes From Your Bank Account Save the confirmation.
EFTPS. The Electronic Federal Tax Payment System requires enrollment that can take up to five business days, but it keeps a 15-month payment history and offers email tracking.11Internal Revenue Service. EFTPS: The Electronic Federal Tax Payment System If you’ll be paying every quarter, the tracking is worth the setup.
Credit or debit card. Processed by IRS-authorized third parties. Credit card fees run 1.75% to 1.85% of the payment (minimum $2.50); debit card fees are a flat $2.10 to $2.15 per transaction, depending on the processor.12Internal Revenue Service. Pay Your Taxes by Debit or Credit Card or Digital Wallet On a $10,000 payment, the credit card fee alone runs $175 to $185.
Check or money order. Make it payable to “United States Treasury,” write your Social Security number and “2026 Form 1040” on the payment, and mail it with Form 1040-V (for a balance due) or the detachable voucher from Form 1040-ES (for an estimated payment) to the address in the form instructions.13Internal Revenue Service. Form 1040-V, Payment Voucher Paper payments don’t produce instant confirmation, so watch your bank statement over the next two to three weeks to make sure it cleared.
Report the Gain on Your Return
Your brokerage sends you Form 1099-B after year-end showing proceeds, cost basis, and holding period for each sale.14Internal Revenue Service. Instructions for Form 1099-B, Proceeds From Broker and Barter Exchange Transactions Starting with the 2026 tax year, digital asset transactions handled by brokers arrive on Form 1099-DA.15Internal Revenue Service. About Form 1099-DA, Digital Asset Proceeds From Broker Transactions
From there:
- List each sale on Form 8949 with description, acquisition and sale dates, proceeds, cost basis, and gain or loss.
- Summarize the totals on Schedule D, where short-term and long-term results net against each other.
- The net capital gain from Schedule D flows to line 7a of Form 1040.16Internal Revenue Service. Schedule D (Form 1040), Capital Gains and Losses
The IRS receives its own copy of every 1099-B, so mismatches between what your broker reported and what you enter trigger automated notices. If a reported cost basis is wrong (common with transferred shares), correct it on Form 8949 using the column (f) adjustment code and the adjustment in column (g) rather than silently entering a different number.
What Late or Short Payment Costs
Two charges run at once. The failure-to-pay penalty is 0.5% of the unpaid tax for each month or partial month the balance is outstanding, capped at 25%. Interest also accrues daily at the federal short-term rate plus three percentage points, compounded daily, and the IRS resets that rate each quarter.17Internal Revenue Service. Topic No. 653, IRS Notices and Bills, Penalties and Interest Charges
Filing on time and requesting an installment agreement drops the monthly penalty to 0.25%. Failing to file and failing to pay together can run to 5% per month in combined penalties, and if the IRS issues a notice of intent to levy, the failure-to-pay rate doubles to 1% per month.
State Tax Still Applies
Federal is only part of the bill. Most states tax short-term gains as ordinary income at rates ranging from under 3% to over 13%; a handful of states have no income tax at all. State estimated payment schedules often mirror the federal quarterly dates, but rates and deadlines vary, so check your state revenue department for the specifics that apply to you.