Guides
The math of investing, explained with numbers you can check. New articles linked to our calculators.
How Much Should Your Emergency Fund Be?
3–6 months of essential expenses — how to calculate it, where to keep it, how to build it.
Read guide → Sep 2, 2026What Is the Average Stock Market Return?
The long-run average — 10% nominal, 7% real — and how to use it without fooling yourself.
Read guide → Sep 1, 2026What Is Dollar-Cost Averaging?
The simplest investing discipline there is — the same amount, on a schedule, no matter what the market does.
Read guide → Sep 1, 2026How Long to Double Your Money
The Rule of 72 in one line: divide 72 by your return. See the full table and how accurate it really is.
Read guide → Sep 1, 2026Is $500 a Month Enough to Invest?
$500 a month at 7% builds $86,542 in 10 years and $609,985 in 30. Whether it's "enough" depends on the goal.
Read guide → Sep 1, 2026What $500 a Month Grows To in 30 Years
Over a working career, $500 a month becomes about $609,985 at 7% — 70% of it from compounding.
Read guide → Sep 1, 2026What Is Coast FIRE?
The point where your invested money can finish the job alone — and what the coast number really means for your plan.
Read guide → Sep 1, 2026How to Grow $10,000 to $100,000
At 7% alone it takes ~34 years; add $500 a month and it takes about 10. Two very different paths to a 10x goal.
Read guide → Sep 1, 2026Can You Retire on $1 Million?
$1 million at a 4% withdrawal rate supports about $40,000 a year. How inflation and your spending change the answer.
Read guide → Sep 1, 2026What $10,000 Could Grow To
A single lump sum at 7% grows to $38,697 in 20 years and $149,745 in 40 — returns side by side, ready to run.
Read guide → Sep 1, 2026How to Reach $1 Million
The math of a million: how monthly contributions, returns and time combine — and why the last decade is where most of the growth happens.
Read guide → Sep 1, 2026What $100 a Month Grows To in 20 Years
A small, consistent contribution becomes $52,093 at 7% — more than half of it from compounding, not your own money.
Read guide → Sep 1, 2026How Does Inflation Affect Your Savings?
At 3% inflation, $10,000 in cash loses about 45% of its buying power over 20 years. Why "safe" cash can be the riskiest long-term plan.
Read guide → Sep 1, 2026How to Save $10,000 in a Year
$833 a month, about $192 a week, roughly $27 a day. A realistic breakdown — and where the same habit can grow over decades.
Read guide → Sep 1, 2026VOO vs VTI: Which Should You Choose?
Both charge the same 0.03% expense ratio, so fees won't decide this one. The real difference is market coverage — and why owning both is usually unnecessary.
Read guide → Sep 1, 2026Debt Snowball vs Avalanche
The snowball wins on momentum, the avalanche on math. See the worked example — $1,267 in interest and 2 months apart on a $12,500 debt.
Read guide → Sep 1, 2026ETF vs Mutual Fund: What's the Difference?
ETFs trade all day; mutual funds once a day. See how they differ on fees, tax and minimums — and where the real cost compounds.
Read guide → Sep 1, 2026The Compound Interest Formula, Explained
A = P(1 + r/n)^(nt), broken down variable by variable — plus worked examples showing how compounding frequency changes the result.
Read guide → Sep 1, 2026How to Calculate Your Net Worth
Net worth is everything you own minus everything you owe. Here's the simple formula, a worked example, and why it matters.
Read article → Aug 28, 2026Compound Interest vs Simple Interest: What's the Real Difference?
Simple interest pays you on your original money only. Compound interest pays you on your growth too. The gap grows quietly — here's the math.
Read article → Aug 28, 2026How Much Should I Save Each Month?
The answer depends on three numbers: your goal, your time horizon, and your expected return. Here's exactly how the math works.
Read article → Aug 28, 2026How Much Will $1,000 a Month Grow in 20 Years?
A $1,000 monthly contribution compounds into a serious number: about $520,927 at 7% over 20 years. Here's the year-by-year math.
Read article → Aug 28, 2026How Much Will $500 a Month Grow in 20 Years?
$500 a month at 7% can grow to about $260,463 in 20 years. Here's the exact math and what it's really worth after inflation.
Read article → Aug 28, 2026How Much Do I Need to Retire at 60?
Retiring at 60 with $3,000/month spending needs about $900,000 saved. Here's the target table and how to get there.
Read article → Aug 28, 2026How Much Will $100,000 Be Worth in 10 Years?
At 7%, $100,000 grows to about $200,966 in 10 years — but after inflation it buys less than you think. Full table inside.
Read article → Aug 28, 2026What Is the Rule of 72? A Quick Way to Estimate Doubling Time
Divide 72 by your annual return to estimate how long your money takes to double. Here's the math, when it's accurate, and a table for every common return rate.
Read article → Aug 28, 2026What Is the 4% Rule? How to Calculate Your FIRE Number
The 4% rule turns your annual spending into a target number and a timeline. Here's how to calculate your FIRE number — and how long it takes to get there — with the math and the caveats.
Read article → Aug 27, 2026How Much Do Investment Fees Cost Over 20 Years?
A 0.5% expense ratio sounds tiny — until you see what 20 years of compounding fees does to your final balance. Here's the real dollar cost, with numbers you can reproduce.
Read article → Aug 27, 2026What Will $100,000 Be Worth in 20 Years?
Inflation silently eats a big chunk of your savings. Here's exactly what $100,000 today will buy in 20 years at 2%, 3% and 5% inflation — with numbers you can reproduce.
Read article → Aug 27, 2026What You Get from Caspenda — 5 Ways Our Free Calculators Help You Invest Smarter
Free investment calculators all look the same. Here's what Caspenda actually gives you — goal planning, transparent math, honest inflation adjustments, and a privacy promise most calculator sites won't make.
Read article → Aug 26, 2026Compound Interest, Explained: How Small Monthly Contributions Become Life-Changing Money
The math behind the most powerful force in personal finance — with real numbers you can check on our calculator.
Read article → Aug 26, 2026DCA vs Lump Sum: Which Is Better?
Run the math on $60,000 invested all at once versus spread across a year — and what the constant-return model can and can't tell you.
Read article → Aug 26, 2026How Much Do I Need to Retire?
The two-number answer to retirement planning — what your savings grow to, and how much you can safely withdraw — with reproducible numbers and honest assumptions.
Read article → Aug 26, 2026How Much Do I Need to Save Each Month to Reach a Goal?
Work backwards from any target — $250k, $500k, $1M — to the exact monthly contribution you need, with numbers you can reproduce on our savings goal calculator.
Read article → Aug 26, 2026Monthly vs Daily Compound Interest: How Much Does Frequency Matter?
Does daily compounding meaningfully beat monthly? We run the real numbers on a typical savings plan — and the answer may surprise you.
Read article → Aug 26, 2026Understanding Your Loan Payment
The equal monthly payment hides a lot — why early payments are mostly interest, how term and rate change your total cost, and how to compare loans honestly.
Read article → Aug 26, 2026What Happens If You Invest $500 a Month for 10 Years?
The exact numbers on steady monthly investing — what $500 a month becomes after 10 years at 7%, and why the last few years do most of the work.
Read article → Aug 26, 2026What's My Real Investment Return?
Your account statement's "return" hides when you added money. Learn how to work backwards from what you invested and what you ended with to your real money-weighted return.
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