Managing money in Bhutan is simple if you carry a little cash and understand how cards and currency work.
Currency
The national currency is the Ngultrum (Nu), pegged one-to-one to the Indian Rupee. Indian Rupees are accepted almost everywhere too — with the exception of the 500 and 2000 notes, which are not legal tender in Bhutan. US dollars are widely accepted at hotels, handicraft emporiums and for tips.
Cards, ATMs and tipping
ATMs in Thimphu, Paro and other main towns accept international Visa and Mastercard, but they are not always reliable and can run out of cash, so never depend on them entirely — carry some cash as backup. Larger hotels and shops accept credit cards, usually with a small surcharge of around 3–4%. Because your tour already includes accommodation, transport, meals and entry fees, you mainly need spending money for drinks, souvenirs and tips for your guide and driver, which are customary and much appreciated.