Understanding H%: How California Courts Calculate and Prove the Time-Sharing Adjustment in California Child Support

California’s Guideline Formula assigns significant weight to H%—the percentage of time the high earner has primary physical responsibility for the child. But H% is not simply custodial hours. Courts look to who actually bears day-to-day responsibility during times when neither parent is physically present: transportation, school involvement, emergency contacts, childcare arrangements, and real-world logistics. Understanding these indicators—and assembling the right evidence—can meaningfully shift guideline support. This article breaks down how judges determine H%, what “primary physical responsibility” really means, and how attorneys can correctly prepare and prove a time-sharing adjustment rather than relying on fairness arguments or reimbursement theories.