Increase the maximum relationships (master-detail plus lookup) allowed per object

The maximum relationships per object equals the total number of lookup and master-detail Relationship fields allowed on a single object.

• You can request to increase the number of lookup fields allowed per object.
• Two (2) master-detail relationships is the maximum allowed.

Default Limit: 40
Maximum Hard Limit: 50

=====

How to check your current limits:

In Salesforce Classic

1. Click Setup.
2. Enter the object of your choice in the Quick Find box.
3. Click Limits.
4. Check the limit on the Custom Relationship Fields row.

In Lightning Experience

1. Click the gear icon.
2. Click Setup.
3. Click Object Manager.
4. Select the object of your choice.
5. Click Object Limits.
6. Check the limit on the Custom Relationship Fields row.