Someone searched for this and found my blog and I haven’t included anything on cost of living in my posts, so this is what I know:
Every state is different. Look up your state’s child support office and look for the guidelines on modification. From what I remember cost of living was included on Vermont’s reasons to modify.
Every state also updates their calculator used to determine the base guideline for support, every year or every few years. The amount you can receive will change accordingly, but only if it goes to court for a modification. This update includes cost of living.
Also, in Vermont, where my case is, they will automatically review your case every three years. For me, that’s a load of crap because they let him file for a review every few months just to annoy the crap out of me and cause stacks of paperwork for my caseworker, whom I have apologized to.
If the increase is at least 10% more than the amount was before you can file for a modification and should be able to get it. Anything less and they consider it a waste of court time.
Here are the state links to child support offices.