Will Emirates accept one 25kg bag instead of two 23kg bags?

No. Emirates is very strict about their baggage allowance. They will charge you for being less than one kilo over the limit.

The best bet is to move 2kg onto your carry-on, if that keeps you within the weight limit, or onto your own self (as I did just earlier this year when flying Emirates) since that weight does not get weighed. Unfortunately, unless traveling in Business class, Emirates does not allow a personal item, so what you add must fit within your carry-on.

While this is not always possible, you can sometimes book both flights on the same ticket and get rules for the most significant carrier to even out the allowance on both segments. Unfortunately, it is only always possible due to a lack of agreement between airlines. This happened to me and I had to scramble to fit within the Emirates allowance luggage that all my other flights of the trip accepted.

Emirates does allow passengers to buy additional checked luggage allowance if so needed. There is a maximum which depends on the ticket and flight.

This is an alternative strategy given there is at least a significant risk the Emirates will charge significantly for the overweight bag.

Use a small foldable duffle bag or similar. For the Emirates flight, which allows two checked bags, put enough in the duffle to get your suitcase under 23 Kg. Make sure the duffle has proper luggage tags, and check it along with your suitcase. That gives you two pieces of checked baggage, both under 23 Kg, conforming to the Emirates rules.

At Mumbai, move the contents of the duffle to the suitcase. Fold it up and also pack it in the suitcase or, especially if it is heavy, abandon it. Now you have one piece of checked baggage, meeting your domestic flight rules.

Emirates will charge you if you are over the bagage limit, this limit has been set by IATA (International Air Transport Association) to protect the health and safety of airport workers. If you go over this limit only so slightly the people down in the bagage handling system have to lift your bag together thus increasing the cost of processing your bag. For this the airline receives an extra charge which they are willing to pay in some cases for their Business class or first class passengers (different limits per class or membership level are on the airlines websites).

To solution is just to spilt your luggage over 2 suitcases and check them both in. Taking the extra load inside the cabin is not handy as there are also weight limitations for carry on luggage.

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