How often can you request a child support modification?

Well, that answer depends on why you are wanting the modification. I know that sounds so much like lawyer double talk but let me explain why it is not (or maybe show why we cannot always give a simple answer to an abstract question).

IC 31-16-8-1(b) sets out how often a child support order may be modified:

Except as provided in section 2 of this chapter, modification may be made only:

(1) upon a showing of changed circumstances so substantial and continuing as to make the terms unreasonable; or

(2) upon a showing that:

(A) a party has been ordered to pay an amount in child support that differs by more than twenty percent (20%) from the amount that would be ordered by applying the child support guidelines; and
(B) the order requested to be modified or revoked was issued at least twelve (12) months before the petition requesting modification was filed.

The yearly restriction of (b)(2) does not apply to (b)(1). What make a change substantial and continuous? Now that depends on the facts of the case.

With a statute containing language like this one, giving an answer depends on the facts and is why "depends" is often an answer heard from many a lawyer.

By the way section 2 referred to above is IC 31-16-8-2 which allows modification of a support order if there is insurance coverage available through the payor's employment or "available at reasonable cost to the parent...."