From frappe/erpnext/wiki/Supported-Versions page ,
As a general principle, from Version 10 onwards, we plan to support each major version for at least 3 years from date of release. The reason for this is that companies that have significant customization on top of ERPNext should be not be forced to move to new releases immediately.
For contributors, this means that separate pull requests for bug fixes and security fixes must be sent for each of the supported versions.
Here is the support plan for major versions that are being supported now:
Version Branch EOL 10 v10.x.x. End of 2020 11 master End of 2021 12 develop Not Yet Released Note: Fixes to Version 10 will not automatically be merged in Version 11, and so on.