A domestic letter with insufficient postage is not always returned to its sender first. Japan Post describes both return to sender and delivery with the recipient paying the shortfall; if the recipient is absent or refuses payment, the item may be returned. Your next step therefore depends on whether you are holding your own returned letter or a notice about mail sent to you. Japan Post: what happens to an underpaid letter
This is a guide to ordinary domestic letters, based on official desk research. It does not cover international postage-due calculations, customs charges, or cash-on-delivery purchases.
Identify the problem before buying more stamps
Keep the envelope and any attached card or slip together. Look for 料金不足, meaning insufficient postage, and distinguish the following situations.
| What you have | The task to resolve |
|---|---|
| A letter you sent has come back | Correct the mailing before sending it again |
| A letter addressed to you has a shortfall notice | Decide whether to accept it and follow the notice's payment instructions |
| A payment notice whose purpose is unclear | Have the postal counter identify the charge before treating it as missing postage |
The same-looking amount does not make these the same task. Adding stamps to a returned item and paying a recipient-side notice are different actions. Use the instructions on the notice you actually received; this guide does not assume that every notice uses one payment method or deadline.
If your own letter came back, check the category again
Read the reason for return before assuming the only problem was an old stamp denomination. The current basic domestic postage is ¥110 for a standard-size letter up to 50 g. A non-standard letter within the specified size limits costs ¥140 up to 50 g. Size and thickness can therefore change the amount even when the weight is the same. Japan Post: domestic letter rates
Here are two hypothetical calculations. Both assume ordinary service, ¥84 of valid postage attached, and that the stated category has been confirmed.
| Mailing category | Required base postage | Attached postage | Calculated difference |
|---|---|---|---|
| Standard-size letter, within 50 g | ¥110 | ¥84 | ¥26 |
| Non-standard, within specified size, within 50 g | ¥140 | ¥84 | ¥56 |
The arithmetic is required postage − valid postage attached. The useful part is choosing the correct first number. Adding ¥26 automatically would still leave the second example ¥30 short. Optional services would require a separate check; they are excluded from these examples.
Recheck the sealed item’s outside dimensions, thickness and total weight. Keep any postal markings and the return notice intact. If the correction or the treatment of the existing stamps is unclear, take the complete item to the counter before remailing it. The calculations above explain a shortfall; they do not authorize peeling off, reusing or disregarding cancelled stamps.
If you are the recipient, decide before opening unwanted mail
If you want to accept the letter, follow the postage-due notice for the amount, payment route and any deadline. When those instructions are difficult to read, bring both the letter and the notice to the postal counter. A useful phrase is:
料金不足の案内が付いていました。支払い方を教えてください。
“There was an insufficient-postage notice attached. Please tell me how to pay.”
This is an example phrase prepared for this guide, not a quotation from Japan Post or a record of a counter visit.
If the item is unwanted, do not open it first and assume you can refuse it afterward. Japan Post’s general refusal procedure for mail it delivered uses a note saying 受取拒絶, with the refusing recipient’s signature or seal, attached to the item. It may be handed to the carrier, taken to a postal counter or put in a postbox. The procedure is unavailable after opening the item and does not apply to items delivered by other carriers. Japan Post: refusing unwanted mail
If a postage-due notice gives its own refusal instructions, show that notice to the counter when uncertain. Do not silently set it aside and assume the charge or delivery has been resolved.
A corrected amount does not restore the original schedule
A returned letter still needs to be sent again. If it concerns a deadline, review the recipient’s submission requirements before remailing it; paying the difference does not by itself establish when it will arrive.
For future letters, calculate postage from the completed envelope instead of copying the stamp value used on an earlier letter. When the category is uncertain, asking the counter to weigh and measure the item addresses the cause of the shortfall before another trip through the mail.