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What Happens If You Underpay Postage?
Underpaid mail can be returned, held for postage due, or delayed. Here's exactly what happens and how to avoid it.
Short answer: your letter probably won’t get thrown away — but it can be returned to you, held for the missing amount, or delayed. Here’s exactly what happens and how to avoid it.
How Much Postage Does a Letter Need?
A standard First-Class letter (up to one ounce) needs one Forever stamp, worth $0.82 as of July 12, 2026. Each additional ounce costs extra. If your envelope is heavy, rigid, square, or oversized, it may also need more postage.
Not sure how many stamps you need? See how many Forever stamps you need.
What the USPS Does With Underpaid Mail
When a piece of mail has too little postage, one of a few things happens:
- Returned to sender. If there’s a return address, the letter often comes back marked “Returned for Postage.”
- Postage due. The recipient may be asked to pay the shortfall before delivery.
- Delayed. The piece sits in processing while the shortage is resolved.
For legitimate mail, the cost of fixing it is small — but the delay can matter, especially for bills, invitations, or time-sensitive documents.
Common Reasons People Underpay
- Assuming a heavy card ships at the letter rate
- Forgetting the extra-ounce charge on a thick invitation
- Mailing a square or rigid envelope at the standard rate
- Using an old denominated stamp below the current rate
How to Avoid Underpaying
- Weigh anything thicker than a few sheets.
- Add one stamp per extra ounce.
- Use a Forever stamp so future rate hikes don’t leave you short.
Ready to Never Run Short Again?
Stock up on discount Forever stamps so you always have the right postage on hand. If you mail in volume, buying Forever stamps in bulk keeps your per-stamp cost down.