At the same time as applying for a place on the Erasmus programme, students also apply for an Erasmus+ grant. 
The grant should be used to cover the additional costs associated with studying abroad.
For the monthly instalments, a distinction is made between three groups of countries (groups 1, 2 and 3).

Probably there will be a maximum length of funding, which might be shorter than the actual stay abroad. There might also be students without funding, so called zero grant students.

The calculation is made to the day (daily rate: monthly rate/30 days). Funding is only paid for days of ‘active study’, which is considered to be from the first day of lectures to the final examination. 
 

Monthly rates for Erasmus Traineeship (SMP, student mobility for traineeship/placement):

Students with an internship place in one of the Erasmus Programme countries (EU + Macedonia, Serbia, iceland, Liechtenstein, Norway, Turkey), which lasts at least 2 months can apply for the Erasmus Traineeship funding. 
The monthly rates for Erasmus Traineeship is made up of the basic monthly grant for Erasmus Studies plus a 150€ Traineeship topup, in each country category. The Erasmus Traineeship grant can be combined with the green mobility topup and the fewer oppurtinities topup.

There is another top-up for "green" mobility: 50 Euro (single payment) + up to 4 travel days if applicable.

Students with a disability, students with child/ren, students, who are first generation academics and working students can apply for additional funding.

Criteria for additional financial support for Erasmus students with fewer opportunities in English here and in German here