What this calculator is measuring
The savings side of the model starts with the current 529 balance, adds recurring monthly contributions, and applies a constant annual return assumption until the beneficiary reaches college. That produces a projected balance at enrollment, along with the split between contributions and investment growth.
The cost side of the model compounds a current annual college cost forward by the chosen annual college-cost inflation rate, then repeats that process across the expected years in school. Comparing the two projections creates a funding-ratio view: how much of the modeled college-cost path the projected 529 balance might cover.