Investing guides

U.S.-focused explainers on 401(k)s, Roth IRAs, cash reserves, and compounding — written to be used with the calculator, not instead of judgment.

401(k) vs Roth IRA
September 7, 2026
401(k) vs Roth IRA: Where Should Your Next $500 Go?
Take the match, then a Roth IRA, then raise the 401(k). 2026 IRS limits and the exceptions that actually matter.
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 Emergency fund vs investing
September 7, 2026
Emergency Fund vs Investing: Which First?
3–6 months in a high-yield savings account, with one exception: do not skip a 401(k) match to fill the cash pile faster.
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 The 4% rule
September 7, 2026
The 4% Rule: How Much Do You Need to Retire?
$40,000 a year from the portfolio is about $1 million at 4%. When FIRE and bear-market retirements need a lower rate.
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 S&P 500 historical returns
September 7, 2026
S&P 500 Historical Returns: Why 8% Is a Planning Number
Long-run averages near 10% before inflation hide lost decades. Run your plan at 8%, then at 5%.
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 How to start investing $500 a month
Updated September 7, 2026
How to Start Investing $500 a Month
Match, debt, cash, then automate a low-cost index fund. Compounding only works if you can keep the $500 going.
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 How to use the compound interest calculator
Updated September 7, 2026
How to Use This Calculator Without Fooling Yourself
The four inputs, what 8% means, and why contributions vs growth is the number to watch.
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