All nationalities except Indian will need a visa to enter Nepal. For that, you’ve to apply for Nepalese visa in the first place and fill the form. This requires a photocopy of your passport valid up to 6 months from the time you apply and 2 passport size photographs. It is after that you’ll pay your visa fee that relies on the length of your stay in the country.
Arrival Visa Fee at different entry points for various length of stay
$25 or equivalent exchange NRS for 15 days
$40 or equivalent exchange NRS  for 30 days
$100 or equivalent exchange NRS for90 days
SAARC nationals are exempt to visa fee for up to 30 days
Visa Extension
For the extended length of 15 days in Nepal, you’ll be charged a visa fee of $30 or equivalent convertible Nepalese Rupees.
If you want to stay in Nepal after even 15 days then you’ll have to USD 2 per day from there onward