Most Muslims pay 2.5% of their income as is specified in the sahih hadith.
It is an obligation on Muslims to pay 1/40 (2.5%) of the wealth which they have had for a full lunar year, 1/40 (2.5%) of goods used for trade, and 5% or 10% of certain type of harvests depending on irrigation. Exempt from Zakat are a person's house and personal transportation.
Zakat is not mandatory on harvest if the total did not reach the minimum limit (nisāb) of about 653 kg (1,440 lb) of crops, nor on gold amounts if the owner has less than 85 g (3.0 oz) of gold or less than 595 g (21.0 oz) of silver.