Linking Nether Portals

Create a portal in the overworld. Step in the portal and take note of the coordinates. Supposedly the Z coordinate doesn't matter.

Divide the X and Y coordinates by 8. This is the corresponding nether coordinates.

Go to the nether using another portal. Navigate to the coordinates and build a portal. Light up this portal but DO NOT STEP THROUGH.

Return to the overworld using a different portal and navigate back to the new overworld portal.

Light up the overworld portal and step through it.