According to Microsoft's lifecycle pages:
| Product |
Mainstream support ended |
Extended support ends |
| Dynamics AX 2012 and AX 2012 R2 |
October 2018 |
Ended April 2022 |
| Dynamics AX 2012 R3 |
October 2021 |
Ended January 2023 |
| Dynamics NAV 2017 |
January 2022 |
January 2027 |
| Dynamics NAV 2018 |
January 2023 |
January 2028 |
After extended support ends, Microsoft no longer provides security updates for that product. The software keeps running, but every month on an unsupported system adds risk: security exposure, compatibility problems with newer operating systems and databases, and fewer partners and people who know the product.
If you are on AX 2012, you are already on unsupported software. If you are on NAV, the deadline is close enough that a project started today would not finish long before it.