How the maths works
How to use it
- Enter your starting balance and monthly contribution.
- Set your time horizon. This field does more work than the contribution size — change it and watch.
- Read the conservative row first. A plan that only survives the optimistic row is not a plan.
A worked example
$1,000 to start plus $250 a month over 25 years lands near $152,000 at 5%, $207,000 at 7% and $332,000 at 10%. The spread between the low and high case is larger than the entire amount contributed. Anyone quoting you a single confident number for 25 years out is quoting the middle of that spread and calling it a fact.
Where this sits in the Financial Literacy resource
A calculator tells you where you are. It does not tell you what to do next, and a number without a plan behind it tends to produce anxiety rather than progress. These stages are free, need no account, and cover the decision this calculator is measuring.
Common questions
Why show three returns instead of one?
A single figure implies a certainty that does not exist. Markets deliver their long-run average in almost no individual year — they overshoot, undershoot and occasionally fall hard. Seeing the spread is what lets you build a plan that survives the bad case rather than one that only works if everything goes right.
What is a realistic long-term return?
Broad US stock indexes have historically returned roughly 10% a year before inflation and around 7% after, measured over multi-decade periods. Shorter periods vary enormously, including decade-long stretches of very poor returns. Past performance does not guarantee future results.
Does this account for taxes and fees?
No. It is a clean model of contributions and compounding. Real returns are reduced by fund expense ratios, trading costs and tax on gains outside a retirement account. Low-cost index funds and tax-advantaged accounts like a Roth IRA exist specifically to keep more of the modelled return.
What this calculator is not
It is an educational model, not a projection and certainly not advice. It knows nothing about your income, your state, your debts or your benefits status, and it ignores taxes and fees unless the page says otherwise. If you receive SSI or SSDI some of this maths works differently and getting it wrong can cost you eligibility — start with the Disability Wealth Guide instead. Our sourcing and correction policy is on the editorial standards page.
Nothing here is stored. Every calculation runs in your browser. No numbers are transmitted, logged or saved to any server, and no account is required. Close the tab and it is gone.