Extensions fail for boring reasons. Here are the ones we see, ranked by how much they cost.
Filing it late
An extension request filed April 16 is not an extension. It is a late return without the return. The failure-to-file penalty starts from April 15. Fix: file the return as fast as possible and ask for first-time abatement.
Not paying
Covered on its own page, because it is the big one. The extension protects you from the 5 percent penalty and nothing else.
Wrong form for the entity
A single-member LLC taxed as a sole proprietorship uses Form 4868, because its income is on the owner's 1040. An LLC taxed as a partnership uses Form 7004 with code 09. An LLC that elected S corporation status uses 7004 with code 25. Filing 4868 for an entity that files its own return extends nothing.
Wrong tax year
Extensions filed in April 2027 are for the 2026 tax year. Software defaults usually get this right. Paper forms and payment portals do not.
Name and number mismatch
The most common rejection reason for e-filed extensions is a name that does not match Social Security or IRS records. A rejected extension can be corrected and resubmitted, but only if you notice, and only within the window the IRS allows after rejection.
Forgetting the state
The IRS does not tell your state you extended. See state extensions.
Forgetting the owners
Extending a partnership or S corporation does nothing for the partners and shareholders. Each files their own 4868.
Missing the extended deadline
October 15 and September 15 are hard stops. Miss them and the penalty is computed from the original date.
Common mistake
The one that makes all the others worse: not keeping proof. An e-file acknowledgment or a payment confirmation number is the only evidence that you extended. Without it, a penalty notice is your word against the IRS's records.
Ready to file it?
You can file a personal extension (Form 4868) or a business extension (Form 7004) online in a few minutes with TaxExtension.com, an IRS-authorized e-file provider operated by our publisher. The extension is automatic; the payment is still due on the original date.
Sources
- IRS, About Form 4868
- IRS, About Form 7004