Recalculate X and Z
From the Overworld to the Nether, divide X and Z by 8, multiply back by 8. The sign is preserved. The Y height is not divided and is selected separately taking into account safety and adjacent frames. Reference: Minecraft: Nether and portals.
Example: house X=800, Z=-400 corresponds to Nether X=100, Z=-50. Do not round negative coordinates to positive ones. In a long tunnel, signs should show the measurement and both pairs of coordinates.
Place both frames manually
Save the coordinates of the home opening, enter and prepare a protected area at the calculated X/Z Nether. If the automatically created exit is far away, build a new one closer to the goal. Choose a height that is accessible, but close to the paired portal vertically if there are competitors nearby.
Check three transitions: house → desired Nether frame → house → same frame. Only after success, dismantle the unnecessary time frame. Until then, save the flint and obsidian on both sides.
Covering the first frame and returning is described here: Your first Nether trip: secure a portal and find your way home.
Two bases require two precise points
For base A (800,-400) target (100,-50); for B (1600,-400) target (200,-50). The difference is 800 Overworld blocks become 100 Nether blocks. If both go through the same frame, first check for the presence of a second exit at the calculated position.
Don't use one universal minimum distance as a guarantee: finding and creating an outlet varies between editions, and Y influences selection. Coordinate the transfer of frames with your neighbors: their route may use the same node.
Recording coordinates and road signs are described in the manual: Maps and signposts: make your world easier to navigate.
