Here's one recommendation from a thread gage manufacturer:
The important thing to take away from this is that the increase in thread pitch diameters will be 4 times your plating thickness. Some thread specifications (for example MIL-S-8879/AS8879) also place a maximum limit on the “pre-plate” thread dimension adjustments that can be taken to accomodate platings or coatings, and require that the thread profile be within tolerance both before (within the permitted “pre-plate” adjustments), and after, plating.
While not mentioned in the above link, realize that the plating thickness on I.D. surfaces (including the threads) can be significantly less the thickness of the plating on the O.D. surfaces of the same part, due to differences in the electroplating current density of these surfaces.
As a result, blindly taking the full permitted plating allowance for internal threads on parts to be electroplated, based on the plating thickness on external surfaces (where it is typically specified and verified), could result in the production of “oversize” internal threads after plating. Conversely, failing to make any adjustment, in conjunction with manufacturing threads at or near the "maximum material" condition, can result in the production of "undersize" internal threads, or “oversize” external threads, after plating...
