Find the net in-migration rate, also known as crude rate of in-migration, the ratio of all migrants who moved into the region (IM) during a given year relative to the total midyear population (p) in the region. Multiply that number by 1,000 to arrive at the crude rate of immigration:
IMR = (IM/p)*1000
Find the net out-migration rate (OMR), also known as crude rate of out-migration, the ratio of all migrants who moved out of the region (OM) during a given year relative to the total midyear population (p) in the region. Multiply that number by 1,000 to arrive at the crude rate of out-migration:
IMR = (OM/p)*1000
Subtract the OMR from the IMR to get the crude net migration rate (CNMR).
For example, say your country has 50,000,000 people. In a particular year, the country received 250,000 immigrants (in-migrants) and lost 55,000 emigrants (out-migrants). The crude net migration rate would be 3.9 migrants per 1,000 people:
[(250,000/50,000,000) x 1,000] - [(55,000/50,000,000) x 1,000] = 5 - 1.1
CNMR = 3.9 migrants per 1,000 people