Official exchange rates are set by the government’s Nepal Rastra Bank and listed in the daily newspapers. Rates at the private banks vary, but are generally not far from the official rate.
There are exchange counters at the international terminal at Kathmandu’s Tribhuvan Airport and banks and/or moneychangers at the various border crossings. Pokhara and the major border towns also have official money-changing facilities, but changing travellers cheques can be time consuming elsewhere in the country, even in some quite large towns. If you are trekking, take enough cash in small-denomination rupees to last the whole trek.
The best private banks are Himalaya Bank, Nepal Bank and Standard Chartered Bank. Some hotels and resorts are licensed to change money, but their rates are lower. Travellers cheques from the main companies can be exchanged in banks in Kathmandu and Pokhara for a 2% surcharge. Euro travellers cheques are also charged a flat US$10 fee per cheque. With each passing year it gets harder to change cheques.
When you change money officially, you are required to show your passport, and you are issued with a foreign exchange encashment receipt showing your identity and the amount of currency you have changed. Hang onto the receipts as you need them to change excess rupees back into foreign currency at banks. You can change rupees back into foreign currency at most moneychangers without a receipt.
Many upmarket hotels and businesses are obliged by the government to demand payment in hard currency (euros or US dollars); they will also accept rupees, but only if you can show a foreign exchange encashment receipt that covers the amount you owe them. In practice this regulation seems to be widely disregarded. Airlines are also required to charge tourists in hard currency, either in cash US dollars, travellers cheques or credit cards, and this rule is generally followed.
In addition to the banks, there are licensed moneychangers in Kathmandu, Pokhara, Birganj, Kakarbhitta and Sunauli/Bhairawa. The rates are often marginally lower than the banks, but there are no commissions; they have much longer opening hours (typically from 9am to 7pm daily) and they are also much quicker, the whole process often taking no more than a few minutes.
Most licensed moneychangers will provide an exchange receipt; if they don’t you may be able to negotiate better rates than those posted on their boards.