Report a missing checked bag before leaving the airport if you can, get the baggage report reference, and file a separate written claim as soon as possible. There is no universal U.S. Department of Transportation "120-hour" deadline for every lost-baggage property claim.

For an international itinerary governed by the Montreal Convention, the usual written-complaint periods are 7 days after receiving damaged baggage and 21 days after delayed baggage is returned or made available. If a checked bag still hasn't arrived 21 days after it should have arrived, you can generally pursue it as a lost-baggage claim under the Convention. A court action under Montreal has a separate, generally applicable two-year limit.

A baggage "refund" can refer to different things:

• a refund of the checked-bag fee;
• reimbursement for reasonable essential purchases while the bag is delayed; or
• compensation for the suitcase and its contents after the bag is treated as lost.

Ask for each item separately. None automatically guarantees the maximum possible payment.

Lost-baggage deadlines at a glance

The European Consumer Centres Network describes the 7-day and 21-day written-complaint periods. The French government's English baggage guidance explains how the ticket or itinerary can identify whether the Warsaw or Montreal Convention applies.

Don't wait 21 days to report the bag

The 21-day point is often confused with the first reporting deadline. It isn't. Under Montreal, it is generally the point at which baggage that still hasn't arrived can be treated as lost for purposes of enforcing the carrier's obligations.

Report the problem as soon as you realize the bag is missing. The airline may locate and deliver it within a few days, but an early report creates a record of when and where the problem occurred. It also connects the tracing file to your later claim for expenses or lost contents.

When the bag arrives before 21 days, the claim will normally be handled as delayed baggage. If the airline declares it lost sooner, ask for the lost-property claim procedure then rather than waiting for the 21st day.

Which rules control the claim?

The answer turns on the itinerary, the carriers involved, and the contract of carriage. A deadline quoted by one airline or website may not apply to your route.

U.S. domestic flights

For an itinerary entirely within the United States, start with applicable U.S. baggage rules and the airline's contract of carriage. The often-repeated "DOT 120-hour rule" shouldn't be treated as a universal five-day deadline for filing a lost-bag property claim.

The carrier may require a particular online form, prompt notice, receipts, and a separate written demand. Its tracing period and internal form deadline are not necessarily the same as a legal limitation period. Report the problem at the airport even if you plan to complete the compensation form online.

An applicable liability ceiling is only a ceiling. It doesn't mean the airline automatically pays that amount. The carrier will usually assess the documented value of the suitcase and contents, subject to the route's limit, valuation rules, exclusions, and the condition of the items. Figures copied from older articles may not be current for every U.S. route.

International flights under the Montreal Convention

The Montreal Convention often governs international carriage when its conditions are met. Its baggage rules treat damage, delay, and loss differently:

• Damage: make a written complaint within 7 days after receiving the baggage.
• Delay: make a written complaint within 21 days after the baggage is placed at your disposal.
• Loss: if the bag hasn't arrived within 21 days after it should have arrived, you can generally enforce the carrier's obligations as a lost-baggage claim.
• Court action: an action under the Convention is generally subject to a two-year limit. The exact starting point is determined under the Convention's rules.

A PIR is useful evidence, but it may not be the formal written compensation claim required by the airline or Convention. Complete the carrier's claim form or send a written demand separately, then save the confirmation.

Montreal expresses the baggage liability limit in Special Drawing Rights, or SDRs, rather than a fixed dollar or euro figure. Currency values and revised limits can make figures in older articles misleading. Your recovery still depends on the loss you can prove; the liability limit is a maximum, not an automatic settlement. A special declaration of interest made when checking the bag may affect the applicable limit.

Warsaw Convention itineraries

Some international trips remain subject to the Warsaw Convention or a related protocol. Its complaint periods and compensation calculations can differ from Montreal's. A cross-border flight does not, by itself, establish that the 21-day Montreal rule applies.

Check the ticket, baggage receipt, and applicable airline conditions. If the governing convention isn't clear, ask the airline to state in writing which convention it is applying and why.

EU261 isn't the main baggage deadline

EU261 is principally associated with denied boarding, cancellations, and qualifying flight delays. It doesn't create a universal flat payment for a lost suitcase.

For baggage damage or delay on a trip covered by Montreal, use the Convention's baggage complaint periods. An EU departure or arrival doesn't automatically replace those baggage rules with an EU261 deadline. The European Consumer Centres Network discusses EU flight-disruption rights separately from Montreal baggage claims.

Airline procedures can add another step

Ryanair, Delta, United, and other carriers don't use one universal claim process. The operating carrier's baggage office normally creates the initial report. On a codeshare or multi-airline itinerary, follow the instructions tied to the PIR and contact the carrier that issued it. If more than one airline handled the bag, keep each carrier's reference number and notify the others as directed.

Delta's baggage guidance, for example, separates bags delayed for five days or less from bags delayed for six days or more and directs customers toward a potential lost-property claim for longer delays. That's Delta's operating procedure, not a general deadline for every airline or jurisdiction.

Don't assume that:

• the PIR itself completes the compensation claim;
• a booking site's deadline is the same as the airline's;
• the airline's tracing period is the legal filing deadline;
• the 21-day loss threshold gives you 21 days to do nothing; or
• travel insurance or a credit-card benefit removes the airline's complaint deadline.

What money can you seek?

Reasonable purchases during a delay

You can generally request reimbursement for reasonable, necessary expenses caused by the delay, such as basic toiletries or replacement clothing. Choose practical items, not luxury purchases, and keep itemized receipts.

The carrier may ask why each purchase was needed, how long the bag was unavailable, and whether you had access to suitable alternatives. There isn't a universal percentage schedule that guarantees reimbursement for every clothing or toiletry purchase.

The suitcase and its contents after loss

Once the bag is treated as lost, prepare an itemized claim for the suitcase and its contents. For each item, include:

• item description and brand;
• approximate purchase date;
• original price and current value;
• proof of purchase when available;
• photographs, serial numbers, or other identifying details; and
• whether it was new, used, damaged, or depreciated before the trip.

The applicable liability limit doesn't guarantee payment up to that amount. Unsupported valuations, luxury items without proof, and items excluded by the carrier's conditions can lead to reductions or denial.

Damage to the bag

Photograph a damaged suitcase before repairing it. Ask whether the airline will arrange a repair, reimburse a reasonable repair cost, or assess a reduction in value. On a Montreal itinerary, send the written complaint within 7 days after receiving the bag.

Checked-bag fees and airfare

A checked-bag fee request is separate from compensation for the suitcase and its contents. Ask the carrier about a fee refund under the rules and policy applicable to your route.

A missing suitcase also doesn't automatically entitle you to an airfare refund. The flight may have been provided even though the baggage service failed. Keep any baggage claim separate from a cancellation, flight-delay, or ticket-refund request.

File the claim in this order

1. Report the missing or damaged bag immediately. Visit the airport baggage service office before leaving if possible. Record the PIR number, bag tag number, flight details, and the representative's name.
2. Submit a written claim. Use the airline's baggage portal or send a written demand if the portal isn't available. Identify whether the bag is delayed, damaged, or lost, and state what you are requesting.
3. Claim necessary expenses as they occur. Attach itemized receipts and briefly explain why each purchase was necessary.
4. Track the tracing file. Save screenshots, emails, text messages, and call reference numbers.
5. Update the status if the bag remains missing. At 21 days under Montreal, or sooner if the airline declares it lost, request the lost-baggage inventory and settlement process.
6. Document the value. Include receipts, order histories, photographs, warranty records, and a clear inventory rather than one unexplained total.
7. Request a written decision. If the airline rejects or reduces the claim, ask it to identify the policy, convention provision, exclusion, or valuation method on which it relied.

If you left the airport without reporting the problem, use the airline's website or contact channel immediately and ask it to confirm in writing that the report was received. Citizens Advice gives the same practical recommendation for passengers who didn't report the issue at the airport. If Montreal applies, you can also say in the written demand that you're "claiming compensation under the Montreal Convention."

If you missed a deadline

Send the claim anyway. A late internal form isn't necessarily the end of the matter, especially if you reported the problem earlier or can show why the deadline was missed.

Include:

• the date and method of the original report;
• the PIR or tracing reference;
• a short explanation for the late submission;
• proof that the airline received earlier messages;
• receipts and evidence of value; and
• a request for a written exception or review.

The airline may accept a late form at its discretion. However, the general two-year Montreal court limit doesn't automatically revive a missed 7-day or 21-day written-complaint period. Nor should the two-year limit encourage you to postpone filing.

For a U.S. flight, use the airline's customer-relations process first. You can then complain to the U.S. Department of Transportation's Aviation Consumer Protection office. A regulator complaint may prompt a response and create a record, but it doesn't guarantee private reimbursement or extend a court deadline.

Travel insurance, homeowners insurance, or credit-card baggage coverage may offer another route. Check the policy or benefit guide for notice periods, deductibles, limits, excluded items, and required documents. These contracts often require prompt notice and don't override the airline's claim rules. Don't seek payment twice for the same loss without telling both the insurer and airline.

Keep the evidence together

Save these items in one folder:

• boarding pass and itinerary;
• baggage tag and description of the bag;
• PIR and other claim numbers;
• photographs of the suitcase and contents;
• delivery date and time if the bag is returned;
• receipts for emergency purchases;
• purchase records or other proof of value;
• copies of online forms and confirmation emails; and
• notes of calls, including dates and representative names.

The practical deadline is today: create the airport report if you haven't already, then submit the written claim. The 21-day Montreal threshold is a point at which to update the claim, not a reason to delay reporting it.