Has something changed that makes you think child support will go up?

There are clear guidelines on what is "supposed to be" submitted. That being said, it really depends on the CS worker. 

Do you have reason to believe that either your DH's income has gone up dramatically or whether BM's has gone down dramatically?  Most state calculators are online and can be used to make estimates based on at least your "guess" of what she makes.

But.. if you are in a situation where your DH made a lot of money on his last tax return and now makes min wage?  you may find that they look into that more.. and they could try to impute income on him.  If BM is making next to nothing and that is a big change, I guess they could do the same there.

By your level of concern, you must think that he is likely to see an increase.  I'm not sure if it's typical to lawyer up for a review or whether it's possible to appeal a decision.. if you cannot appeal.. I guess you have to look at making it right up front.

But lawyers are not cheap.. it would have to be a huge increase that he might have to pay for a long period of time to make that worth it.

typically its a plug in thing. Most states calculators are online. You should be able to get a good estimate. 

Leave it to a twunt hcbm to do something like this over the holdays.  Typical.

Our state has a calculator online.  By the books, it's with a material change or default is a once every 3 year review... IF requested.  Support will change only if the greater of 10% or $50 threshold is met.  2 most recent paystubs and last W2 are needed from both parties.

You're also supposed to self report to FOC change in address, employment, insurance and compensation.  

BM follows none of these but is also the first to cry foul.  Hilariously enough, each time BM gets a wild hair it costs her significant amounts not only in attorney fees but reduced child support. 

She's always convinced SO is out to get her (projection much?) and rebuffs any attempt at cooperation to her benefit.  Always to her detriment.

SO is still with his divorce attorney and keeps him on retainer.  Any time BM gets squirrely, for a couple hundred dollars the attorney advises rather than actively represents SO in order to keep the billables down.  The rare occasion that it actually goes in front of the court, he steps on as representation.

BM, however, drops a retainer on a new attorney every time so has no relationship and seemingly maximizes her charges.

Check out the governing body in your jurisdiction (in MI, ours is Friend of the Court or FOC) so you know the rules and can keep your side of the street clean.  You'll be able to understand if and/or when it's appropriate and necessary (for your case) to consult or seek representation.

BM here is a dimwit so she's not a real threat so much as a hassle, but it's important to know and play by the rules of the game.  Takes a good chunk of the stress out of dealing with her dumb.