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DO you have any ideas from US to Nepal flight ?What would be the average price for Return trip ??/ appreciated yuour replay ??

Only thinking aloud...

Emirates - via Dubai

Qatar Airlines - via Doha

Etihad - via Abu Dhabi.

Search Skyscanner for price comparisons, then book direct with the Airline.

Where in the US are you flying from? LL has given you good suggestions if you are flying from Europe or from the Eastern US, but if you are flying from the west coast, you will be better off flying via Asia changing places in Narita (Tokyo) or Singapore.

Take into consideration the frequent flier program you use, and try to choose a carrier from that alliance. That's a long flight and it would be a shame not to earn miles you can use.

You will likely pay in excess of US$1000 return to Kathmandu.