Birth to 5: the compounding decade
The first dollars compound the longest: $200/month from birth at 6% becomes ~$88k by 18, vs ~$33k if started at 10. This phase is pure accumulation — maximum equity allocation, automate the transfer, claim the state deduction, and let the market do the early heavy lifting. The tuition projection here prices the target; this phase is where it gets cheap to meet.
Ages 6–13: the steady middle
Contributions continue (raise escalations help), the portfolio stays growth-heavy, and the milestones get checked annually. This is also the phase to visit net price calculators for realistic targets — the plan refines as the child's aptitudes and your finances clarify. Falling a milestone behind is normal and fixable; ignoring the account is not.
Ages 14–18: the glide and the decision
The portfolio glides conservative (enrollment money out of equities), contributions peak if possible, and the real list of schools gets priced against the projection. The final two years are cash-flow management: state deductions on peak contributions, grandparent 529 contributions (now aid-friendlier than ever), and the honest conversation about the share the family funds.