An Employer Identification Number (EIN) is the federal tax ID your business uses for filing returns, opening a business bank account, and hiring employees. For US residents with a Social Security Number, applying online through the IRS website is typically the fastest path, often producing an EIN immediately upon completion.
The online application is only available to applicants with a valid SSN or ITIN who are applying as the "responsible party" for the business. If you don't fall into that category, the process shifts to a paper or fax application (Form SS-4), which takes considerably longer, often several weeks, and requires more careful preparation since errors on a paper application are harder to correct quickly, sometimes requiring the entire submission to be redone from scratch.
One detail people frequently get wrong: the "responsible party" listed on the application must be an individual, not another business entity, and that person needs to actually have authority over the entity's funds and assets, not just be a name filled in to complete the form. Getting this wrong is a common reason applications get flagged for follow-up, delaying an EIN that would otherwise have been issued immediately.
An EIN Application Delayed by an Entity Type Mismatch
Consider a small business owner forming a two-person LLC who applies for an EIN online, but selects "sole proprietorship" on the application by mistake, since that's what the business had been informally operating as before the LLC paperwork was completed. The EIN is issued immediately under this incorrect entity classification. Months later, when the business's tax preparer goes to file the LLC's partnership return (Form 1065), the IRS system shows the EIN registered as a sole proprietorship, creating a mismatch that generates a notice and delays the return.
Resolving this requires contacting the IRS directly to correct the entity classification on file, a process that can take several weeks of phone calls and written correspondence, all of which could have been avoided by simply selecting "multi-member LLC" correctly on the original application. A ten-second selection on a form, made carelessly, turned into a multi-week correction process a year later.
Choosing the correct entity type on the application, sole proprietorship, single-member LLC, multi-member LLC, corporation, matters because it determines which tax forms the IRS expects from you going forward. Selecting the wrong entity type here can create a mismatch that causes confusion or notices down the line, since the IRS's system starts expecting a filing pattern based on what was selected at application time, and correcting it after the fact requires direct IRS contact rather than a simple online fix.
Once issued, your EIN never expires and generally does not change even if your business structure changes slightly, though certain major changes, like adding a partner to a single-member LLC or converting to a corporation, do require a new EIN. Keeping the original confirmation letter (CP 575) in a safe place saves real hassle later, since replacing a lost EIN confirmation requires contacting the IRS directly, and banks routinely ask to see it when opening a business account.
The IRS's One-EIN-Per-Responsible-Party-Per-Day Rule
The IRS limits online EIN applications to one per responsible party, per day. If you're forming multiple entities at once, perhaps a holding company and an operating subsidiary, or several single-purpose LLCs, you cannot obtain more than one EIN online under the same responsible party's identity in the same calendar day. This catches business owners forming multiple entities simultaneously off guard, since the second application will be rejected until the next day.
Planning entity formation with this limit in mind, spacing out applications across multiple days when forming several entities, avoids an unnecessary delay right at the start of setting up a new business structure.
It's worth double-checking every field before submitting, particularly the business name and address, since correcting an error after issuance means contacting the IRS directly rather than simply resubmitting the form. A few extra minutes reviewing the application before clicking submit is meaningfully less work than untangling a mismatched EIN record months later when a bank or the IRS flags the discrepancy.