Expanding your business to the US or investing from abroad is incredibly exciting. But dealing with the IRS? Not so much. The rules are confusing, the forms look like they are written in an alien language, and making a simple mistake can cost you thousands of dollars in penalties.

Let’s skip the confusing legal jargon. Here is a plain-English breakdown of the most important US tax forms you actually need to know about, so you can stay out of trouble and keep your business running smoothly.

1. Doing Business in the US? You Need Form 1120-F

If your company is registered outside the US but makes money connected to a US trade or business, you almost certainly need to file form 1120-f.

Here is the catch that trips up a lot of founders: Even if your country has a tax treaty with the US that protects you from actually paying US taxes, you still have to file this form to claim that protection.

Why it matters: If you forget to file or miss the deadline, the IRS can play hardball. They might tax your gross income at a flat 21% and refuse to let you deduct any of your business expenses. You don't want that.

2. Don't Ignore the Details: Schedule OI

If you are an individual living abroad and you need to file a US tax return, you’ll use Form 1040-NR. But there is a very important attachment attached to it called the nonresident alien interest schedule oi (which stands for "Other Information").

This is basically a questionnaire where you tell the IRS about your citizenship, your exact visa status, and the tax treaties you are using to lower your tax bill.

A lot of people rush through this part, but don't skip it. Making a mistake on Schedule OI is one of the most common reasons the IRS delays processing returns. Take your time and fill it out accurately.

3. Paying Foreigners? Meet Forms 1042-S and 945

If your US business pays money to people or companies outside the US (like paying royalties to a foreign creator, or dividends to an overseas investor), the IRS wants to know about it.

• form 1042 s: You use this specific form to report the income you paid to a foreign person or business. Even if you didn’t hold back any taxes from their payment because of a tax treaty, you still have to file this form. It's mandatory.

• 945 tax form: People often confuse this one with the 1042-S. The 945 form is used to report federal income tax that you withheld from non-payroll payments (like backup withholding). It's mostly used when dealing with US residents, not foreigners.

Knowing the difference between these two will save your accounting team a huge headache at the end of the year.

4. Skip the Printer: Sign Your Documents the Easy Way

Dealing with IRS forms means you are going to be signing a lot of documents. Printing out pages, signing them with a pen, scanning them back in, and emailing them is a massive waste of your time.

Instead of doing things the old-school way, you can just use a tool to write signature online and apply it directly to your digital PDFs. It’s legally binding, looks professional, and takes about five seconds.

At BrieflyGo, we know that handling legal documents and contracts can be a nightmare. That's why we build tools to help you analyze risks, automate your paperwork, and get things signed fast so you can get back to actually running your business.

👉 Create your digital signature in seconds

The Bottom Line

US taxes for nonresidents don't have to be a nightmare if you know exactly which forms apply to your situation. Don't leave your IRS reporting to the last minute. Get your documents organized, double-check your treaty benefits, and make sure everything is signed and filed on time.