Calculator + AI-assisted guides
Compound Interest Calculator
See what a starting balance and monthly contributions could be worth. This uses a standard compounding formula. It is a projection, not a promise.
Growth over time
| Year | You put in | Growth | Balance |
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Enter your numbers. A short, rules-based summary will appear here.
Guides worth reading next
Practical U.S. investing topics — 401(k)s, Roth IRAs, emergency funds, and how much you may need to retire.
How to start investing $500 a month
A simple plan: take the 401(k) match, kill high-interest debt, then automate index-fund contributions.
401(k) vs Roth IRA: where the next $500 goes
Match first, then Roth IRA, then back to the 401(k). Here is the order most households should consider.
Emergency fund or invest — which first?
Stock returns are not guaranteed. Credit-card rates are. Use a simple order so a layoff does not become a fire sale.
The 4% rule: how much do you need?
A $40,000 spending year is a $1 million nest egg at 4%. See when the rule helps — and when it breaks.
Frequently asked questions
What is compound interest?
It is interest on both the money you invest and the interest you have already earned. That is why $500 a month looks modest in year 5 and much larger in year 25.
How is the future portfolio value calculated?
Your starting amount compounds monthly. Each monthly contribution is added at the end of the month and then compounds with the rest. If you turn on “today’s dollars,” the ending value is adjusted for the inflation rate you enter.
What is a realistic expected return?
The S&P 500’s long-run average is often cited at about 8%–10% before inflation. Use 7%–8% if you want a more conservative plan. No calculator can tell you what next year will return.
How much should I invest per month?
A common U.S. starting point is: get any 401(k) match, keep 3–6 months of expenses in cash, then invest a fixed amount you can stick with — $200, $500, or 15% of pay. See the $500-a-month blueprint.
Should I invest if I still have credit-card debt?
Usually no, except for an employer match. A 22% card is a guaranteed hole in the bucket. Read the order of operations.
Is this a 401(k) calculator?
It is a growth calculator, not a tax calculator. It does not model employer match, contribution limits, or Roth vs pre-tax. For account choice, start with 401(k) vs Roth IRA.
Where does AI come in?
Guides are drafted with AI assistance, then checked against U.S. tax limits and conservative investing practice. The calculator is a standard compounding formula. The dark “AI takeaway” box only restates the numbers you typed — it does not predict markets. More on the About page.