While travelling to Nepal, we recommend bringing some cash in a convertible currency, such as USD, CAD, AUD, EURO etc. There are ATM machines in cities like Kathmandu, Pokhara, Chitwan (Sauraha only) etc, in which you may be able to use your card (especially MasterCard and Visa). While using ATM machines you will receive cash only in Nepali currency. The ATMs of different banks have different limits per transaction, with some as little as NPR 10,000, and some as high as NPR 30,000. Maestro and American Express cards may not work in all ATMs. Most restaurants, hotels and service providers do accept major cards, but they add a card processing fee of between 2% and 4%. There is an ATM machine in Lukla and Namche Bazaar, but these cannot be relied upon. Some trekking lodges have started accepting payments from cards, but their card processing fee can be up to an additional 10%.
While trekking, we recommend you exchange your foreign currency into Nepali currency in a big city like Kathmandu or Pokhara. Some hotels offer this service, but money changers in shopping areas offer the best rates. Exchange rates are fixed daily by the Nepal Rastra Bank, and the same rate will be followed by money changers and service providers. There will be some service fee or commission on the rates given by the Nepal Rastra Bank.
You will need to carry enough cash for the duration of your trek. There may be a possibility of exchanging your foreign currency into Nepali currency while trekking, but you will receive a very poor exchange rate. For your daily expenses while trekking, please consult your trekking guide or tour leader.
For a general idea on exchange rates, follow XE.com or other sites, but these may not be valid in the markets of Nepal.