Franked Too Much or Too Little Postage? How to Fix It Before Posting
If you have franked the wrong amount, fix it before the item is posted. For under-franked mail, add the missing amount with a second impression. For over-franked mail, do not post it: keep the unused impression and ask Royal Mail about a refund. Once an under-franked item is in the postal system, Royal Mail can recover the shortfall plus an administration fee.
Every mailroom gets this wrong occasionally. A Large Letter franked as a Letter, an envelope that turned out thicker than you thought, or the wrong class selected on a busy afternoon - all of these are easy to do and, caught early, easy to put right. This guide explains what to do in each case and how to stop it happening again.
What counts as under-franked and over-franked mail?
Mail is under-franked when the postage printed is lower than the service, format and weight require. It is over-franked when you have paid for more than the item needs, for example a First Class impression on a letter you meant to send Second Class.
The price depends on the service, the format and the weight, so a mistake in any one of them changes the amount. Our guide to franking the right format explains how Royal Mail separates Letters, Large Letters and parcels, and our 2026 postage rates update lists the current prices.
How to fix under-franked mail before posting
If you spot the error while the item is still in your mailroom, you can top it up with a second impression for the missing amount. The steps depend on your machine.
On a Mailmark franking machine
- Cross through the 2D barcode on the original impression with a black ballpoint pen, taking care not to cover the printed price.
- Write your initials beside it.
- Print a new impression for the correct full amount in the bottom left corner of the envelope, or on a label placed to the left of the original impression.
Crossing out the barcode matters because the Mailmark barcode is scanned by Royal Mail, and two live barcodes on one item cause confusion.
On a standard (non-Mailmark) machine
Print the missing amount in the bottom left corner of the envelope, or on a franking label placed to the left of the original impression. If you are unsure which type of machine you have, check with your supplier.
What happens if under-franked mail is posted anyway?
Under-franked items are usually still delivered, but Royal Mail recovers the missing postage along with an administration fee, either from you or from the recipient. Fee amounts change over time, so check the current figures on the Royal Mail franking page rather than relying on an old figure.
A few mistakes cause most surcharges:
- A Large Letter franked at the Letter rate.
- An item thicker or heavier than the Letter limits.
- A larger envelope, such as C4, franked as a standard Letter.
- International mail franked with a UK rate.
How to deal with over-franked mail
Do not post an over-franked item. Take out the contents and start again with a fresh envelope or label.
You may be able to claim back the value of unused impressions. Royal Mail asks you to return the whole unused envelope or label, and the impression must be clear and readable. Conditions such as minimum claim values, fees and time limits are set by Royal Mail and can change, so confirm them before you submit a claim. Keep a simple log of spoiled items so you can claim in one batch.
How to stop franking mistakes happening
Most errors are caused by the wrong format, the wrong class or an unweighed item. A few habits help:
- Weigh and measure first. Use the scale on your machine or a separate one, and measure thickness as well as weight.
- Sort before you frank. Group mail by destination, service and format. This also helps you keep to Royal Mail's rules for separating mail.
- Check the date. Royal Mail allows franked mail to be posted up to 7 days after the impression is printed, so batches can be prepared ahead. Our guide to dating franked mail correctly covers the details.
- Use suitable envelopes. Poor surfaces can smudge impressions and make a correct frank unreadable. See our advice on the best envelopes for franking machines.
- Keep print quality high. A faint impression can be mistaken for a mistake. If prints look weak, read why your machine prints faint or streaky and make sure you are using the correct ink cartridge for your machine.
Frequently asked questions
Can I just stick a stamp on under-franked mail?
It is better to add a second franked impression or a franking label for the missing amount, following the correction steps for your machine type. If you are unsure, check with your franking machine supplier or Royal Mail first.
Do I need to cross out the barcode when re-franking?
On a Mailmark machine, yes. Cross through the 2D barcode with a black ballpoint pen without covering the price, add your initials, then print the new impression to its left or on a label.
Can I get a refund for over-franked mail?
Possibly. Royal Mail lets you claim back the value of unused, readable impressions if you return the whole unused envelope or label, but its conditions and time limits can change, so check them before claiming.
What happens if under-franked mail is posted?
It is usually still delivered, but Royal Mail recovers the shortfall plus an administration fee. Catching the error before posting avoids the charge.
How long can I keep franked mail before posting it?
Royal Mail allows franked mail to be posted up to 7 days after the impression is printed.
Need the right supplies to keep every impression sharp? Browse our franking machine supplies or find your model's cartridge in our cartridge identification guide.