The carrier counts as oil in my formula — how much do I subtract?

All of it, by mass. A pre-dispersion is a raw material that brings oil with it, and that oil is in the formula whether or not it was counted.

Our dispersions come in several carriers: C12-15 alkyl benzoate (NanoT 4015, 4513, Z-6060), dicaprylyl carbonate (NanoT 4528) and dimethicone (NanoT 2355, Z-6050). Each one lands in the oil phase at the dispersion's carrier fraction.

The arithmetic: work out the filter solids you need, divide by the dispersion's solids content to get the dispersion weight, then subtract the carrier mass from the oil phase. Skipping that step is the usual reason a converted formula comes out greasier and less stable than the powder version it replaced.

Two checks afterwards. Compatibility: the carrier has to be miscible with the main oil phase or it will separate. And skin feel: carriers differ in spread and residue, so the swap is felt even when the numbers match.

Where the formula already uses an ester, choosing a dispersion in the same carrier removes most of the rebalancing. Where it does not, pick a compatible carrier and re-run stability rather than assuming.