Rates & sources
Compound growth assumes reinvested returns and no platform fees. Past performance is not a guide to future returns.
Source: FCA — Investment basics — figures refreshed at the start of each tax year.
When to use this calculator
- Before choosing between saving, investing, or increasing your monthly contribution.
- When you want to compare best-case, base-case, and cautious return assumptions.
- When you need a quick projection before making a longer-term portfolio decision.
- When you are deciding how many more years of contributions are needed to reach a specific target balance.
- When you want to see whether starting earlier versus contributing more each month produces a bigger outcome.
A realistic US planning example
Use these sample inputs as a quick scenario test, then change one variable at a time to compare outcomes.
Child's Current Age
35
College Start Age
35
Current 529 Balance ($)
$1,400
Monthly Contribution ($)
$250 per month
After entering these figures, review projected 529 balance, projected 4-year cost and projected annual cost together rather than in isolation — each metric tells a different part of the story. Then rerun the tool with one input adjusted to see which variable has the biggest effect on all three outputs before you settle on a plan.
How to read your results
Projected 529 Balance
Use this metric to compare scenarios side by side and understand how changes in the key inputs drive the final outcome. If the figure surprises you, isolate one variable at a time and rerun the calculation to identify which assumption is responsible.
Projected 4-Year Cost
Use this metric to compare scenarios side by side and understand how changes in the key inputs drive the final outcome. If the figure surprises you, isolate one variable at a time and rerun the calculation to identify which assumption is responsible.
Projected Annual Cost
Use this metric to compare scenarios side by side and understand how changes in the key inputs drive the final outcome. If the figure surprises you, isolate one variable at a time and rerun the calculation to identify which assumption is responsible.
Funding Gap
Use this metric to compare scenarios side by side and understand how changes in the key inputs drive the final outcome. If the figure surprises you, isolate one variable at a time and rerun the calculation to identify which assumption is responsible.
Coverage
Use this metric to compare scenarios side by side and understand how changes in the key inputs drive the final outcome. If the figure surprises you, isolate one variable at a time and rerun the calculation to identify which assumption is responsible.
Method & assumptionsAuthoritative sources
This calculator projects the growth of a 529 college savings plan using annual compound growth applied to your starting balance plus contributions. Each year, the existing balance and annual contributions are multiplied by one plus your expected return rate, simulating a tax-deferred account where earnings are not reduced by taxes while the money remains invested. Future college costs are projected by compounding today's annual cost at your chosen tuition inflation rate over the years until college begins — historically around 4% per year for US four-year institutions. The four-year total is then compared against your projected balance to show a coverage percentage and any funding gap.
The model does not account for the state income tax deduction many US 529 plan holders receive on annual contributions, which can effectively boost your net return by 3% to 10% depending on your state tax rate. It also does not model year-by-year asset allocation shifts, such as the age-based glide paths most 529 plans offer that automatically move from equities toward bonds as college approaches. Qualified 529 withdrawals are tax-free at the federal level for eligible education expenses including tuition, fees, room and board, and books, making the effective after-tax growth of a 529 plan significantly better than a standard taxable brokerage account for this purpose.
Common mistakes
- !Assuming a constant return without checking a more conservative growth rate.
- !Forgetting to include ongoing contributions, fees, or tax wrappers where relevant.
- !Focusing only on the final balance instead of the path required to reach it.
- !Ignoring the drag of platform fees or fund charges, which can reduce the real compounded return significantly over ten or more years.
- !Comparing ISA and general investment account projections without adjusting for the tax treatment of interest, dividends, or capital gains.
What to do next
- Test a cautious, expected, and optimistic growth rate instead of relying on a single projection.
- Compare this result with related savings or retirement tools before committing more money.
- Use the linked guides to understand which assumptions matter most over longer periods.
- Consider running the same figures in an ISA and a general account scenario to see how the tax treatment changes the outcome over ten or more years.
- If the projected balance falls short of your target, use the tool to work backwards — increase the monthly contribution until the result meets your goal.
Frequently asked
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End-of-article next steps
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