For most of history, judges have applied fault- and sex-based presumptions to decide the kinds of custody arrangements that are in children’s best interests. Now that those have been eliminated, courts have no clear guidance for deciding the custody of children other than a vague directive to do what is “best.” Legislatures have enacted non-exclusive lists of suggested factors to consider, but these statutes are frequently as vaguely worded as the “best interest” directive. Because precatory words inserted into statutes with the intention of guiding a judge’s discretion are not binding, they do not provide a basis for appellate review. The result is that there is ample room for the operation of faulty assumptions and biases, potentially to the detriment of children. A growing body of evidence suggests that children benefit more from equal-time arrangements than they do from other kinds of custodial arrangements. The experiences of jurisdictions that have enacted equal-parenting-time presumptions confirm the benefits of a presumption of equal parenting time. Care must be taken, however, to ensure that the presumption is rebuttable and that it is crafted to be both feasible and maximally beneficial to children. This Article points the way.