The BMS offers funding, both for Phase I (Master) and for Phase II (Doctoral researchers).

Phase I (Master)

Phase I scholarships:

The BMS offers a maximum of 10 BMS Phase I scholarships per years. These are granted for 1+18 months (extendible by 6 months), and amount to 1,000€ per month.
All BMS scholarships are tax-free and do not include health insurance.
In addition to the scholarship, one can earn up to 6,000€ per calendar year without paying taxes. 

Students in Phase I with sufficient German language skills are normally expected to support themselves by other means, either with student jobs like tutoring for undergraduate classes, or by applying for outside scholarships, for instance from the Studienstiftung des deutschen Volkes.

Tutoring / student jobs:

permanent calls:
www.tu.berlin/math/tutor-innen-ifm/bewerbung-als-tutorin
www.mi.fu-berlin.de/public/stellen/tutorentaetigkeit/index.html
www.zib.de/node/5583

other student jobs:
www.jobs.tu-berlin.de/stellenausschreibungen?filter%5Bfulltextsearch%5D=&filter%5Bworktype_tub%5D%5B%5D=stud-mit&filter%5Bworktype_tub%5D%5B%5D=stud-ohne (also look for Beschäftigte in Verwaltung 25% TVL 3 or 4 positions)
www.fu-berlin.de/universitaet/beruf-karriere/jobs/stud/index.html
www.hu-berlin.de/de/service/arbeit/stellen
www.bht-berlin.de/1652/
www.hwr-berlin.de/hwr-berlin/stellenangebote/#c4482
www.htw-berlin.de/beschaeftigte/aktuelles/stellenangebote/studentische-hilfskraefte/

HU master's students can apply for the Humboldt Research Track Scholarships for the last year of their master studies: https://www.humboldt-graduate-school.de/en/promotionsinteressierte-en/uebergangsstipendien/allgemeines


Phase II (Doctoral research)

Phase II Funding

The BMS offers three PhD positions (75% TVL13) for three years each starting in October each year:
- one position for external Phase II applicants
- two positions for Phase I students continuing with Phase II

Phase I students who want to continue with Phase II need to find a PhD supervisor in the last semester of Phase I. The PhD supervisor should provide PhD funding for at least three years or advise on other funding sources and applications.
Applications for Phase II received via the BMS application portal and requiring PhD funding are sent to potential supervisors within the BMS faculty and considered for any open PhD positions in the supervisor's research group.

In addition to BMS PhD funding and MATH+ projects, doctoral researchers can also be funded through other research institutions or graduate programs in Berlin:
• (International) Research Training Groups (RTG)
• International Max Planck Research Schools (IMPRS)
• DFG Collaborative Research Centers (CRC/ SFB)
• Zuse Institute Berlin (ZIB)
• Weierstrass Institute for Applied Analysis and Stochastics (WIAS).

A complete list can be found here: www.math-berlin.de/about-bms/people-a-organization/units
The BMS integrates the above projects and institutions, as well as many others, as Certified Units, Associated Units, Cooperating Research Centers and Research Institutes.

PhD Scholarships

Other scholarships may be available from funding institutions such as
German Academic Exchange Service (DAAD)
Stibet (DAAD)
Studienstiftung des Deutschen Volkes
FAZIT Stiftung (in German)
via exchange programs of the universities (for example, at TU Berlin)
via teaching assistantships (for example, at TU Berlin)
Eva-Wolzendorf-Stipendium (in German, at FU)
Berlin Funding for Graduates (Elsa-Neumann-Stipendium des Landes Berlin)

for women:
The Caroline von Humboldt Grant Programme (at HU Berlin)
Degree completion grants from the Council of the Central Office for Women's Affairs "Promotionsabschlussstipendium (PAS) (at TU Berlin)
Personal financial support (at FU Berlin)

An overview of additional foundations supporting PhD students can be found here:
Center for Junior Scholars (TU Berlin)
Begabtenfoerderungswerke
StipendiumPlus
Research in Germany
Funding opportunities for graduates -- Promotionsportal of FU Berlin

Other Funding opportunities:
Berlin University Alliance - Job Portal
Physikalisch-Technische Bundesanstalt