An extension gives you more time to file. It gives you no more time to pay, and it never has.
That sounds like a limitation until you look at what the two penalties actually cost, at which point it becomes the single most useful thing to know about deadlines: filing late is charged at ten times the rate of paying late. An extension removes the expensive penalty entirely and leaves the cheap one. That is a very good trade, and it is free.
The two penalties are not comparable in size
Failure to file is 5 percent of the tax due for each month or partial month the return is late, up to a maximum of 25 percent.
Failure to pay is 0.5 percent per month or partial month, also up to 25 percent.
Ten to one. Somebody who cannot pay and therefore does not file has chosen the expensive problem in order to avoid the cheap one, which is precisely backwards and is the most common and most costly misunderstanding in this whole area.
Two refinements worth knowing:
- Where both penalties apply in the same month, the failure to file penalty is reduced by the failure to pay amount. So the combined charge is 5 percent a month, not 5.5.
- After five months the failure to file penalty has reached its 25 percent maximum and stops. The failure to pay penalty keeps running.
Interest runs on top of both.
The minimum penalty, which catches small balances
If a return is more than 60 days late, a minimum penalty applies. It is 525 dollars for returns due after 31 December 2025, and was 510 dollars for returns due during 2025. The figure is keyed to the year the return was due rather than the tax year, and it is adjusted for inflation.
The part usually left out is the cap. The charge is the smaller of that floor and 100 percent of the underpayment, so a small balance is not turned into 525 dollars. A return 61 days late owing 300 dollars attracts 300 dollars. What the floor does is remove the benefit of a small percentage once the balance is larger than the floor and the 5 percent a month has not yet caught up, which is the position most late returns with real tax on them are in.
What an extension actually does
Filing the extension form on time removes the failure to file penalty, provided you then file within the extended period.
- Individuals file Form 4868 and get to 15 October.
- Businesses file Form 7004 and get an automatic six month extension. Automatic means granted on filing, not assessed or approved.
What remains is the failure to pay penalty on anything unpaid, at 0.5 percent a month, plus interest. That is the cost of not having the money. It is not the cost of not having the paperwork.
Is there a downside to filing one you do not need
No.
It costs nothing, it is not a red flag, it does not extend anything the IRS can use against you, and it does not have to be justified. If a return is not certain to be complete and correct by the deadline, the extension should be the default rather than the fallback.
The one thing it does not do is excuse payment, which means the useful discipline is to estimate what you owe and pay it with the extension even while the return is unfinished. An estimate that is roughly right leaves you with a small failure to pay exposure rather than a large one.
Two ways to make the failure to pay penalty smaller
Both are worth knowing because they change the rate rather than the amount owed.
An approved payment plan halves it. For an individual who filed on time and has an approved payment plan, the failure to pay rate drops from 0.5 percent to 0.25 percent per month. Note the condition: filed on time. It is another way the filing obligation and the payment obligation are not the same thing.
Ignoring a levy notice doubles it. If the tax is not paid within 10 days after a notice of intent to levy, the rate rises to 1 percent per month.
One more mechanical point: full monthly charges apply even if you pay in full before the month ends. Paying on the first of the month and the twenty eighth cost the same, so there is nothing to gain by waiting out a month you have already entered.
What to do
If the return will not be ready, file the extension and pay your best estimate of the balance. If you cannot pay the balance, file anyway, on time or on extension, and deal with the payment separately. Never hold a return back because of the money.
For entities, the extended deadline arrives in September and carries a penalty structure of its own, charged per owner rather than as a percentage of tax, which is covered in the September 15 deadline for extended business returns.
What a return costs, and what is quoted separately, is set out on the pricing page.