Investment
The eighth wonder of finance: why compounding only works if you wait
Einstein probably never said it, but the underlying math has been the most-broken promise of personal finance for a hundred years.
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Browse all calculators →Invest a fixed sum on a regular schedule and ride out the market’s swings — see what your contributions grow into.
Open → MortgageThe monthly payment on a 30-year mortgage isn’t intuitive, and the full amortization is even less so. See both, side by side.
Open → RetirementHow big a portfolio do you need to withdraw a comfortable annual income for 30 years? A surprisingly simple answer.
Open → ValuationDiscount projected cash flows back to today’s dollars. The math finance professors won’t shut up about — explained.
Open →CrunchCalcs brings every financial calculator you need into one place. Each tool is built around two ideas — that calculators should be easy to use, and that they should explain themselves. Inputs are clear, results appear instantly, and every calculator is paired with a short note on the formula behind it and what the number means in practice.
Simple interest is paid only on your original principal; compound interest is paid on the principal plus all the interest already earned, so it snowballs. Over a year or two the gap is small, but over decades compounding pulls far ahead — which is why it is the engine behind almost every long-term investment.
APR is the simple annual rate that ignores compounding within the year; APY (the effective rate) folds the compounding in, so it is always the higher number. Lenders tend to advertise whichever flatters them — APR on loans, APY on savings — so convert both to the same basis before you compare.
Gross pay is your salary before anything is removed; take-home (net) pay is what actually reaches your account after income tax, social contributions and any deductions. The gap is commonly 20–40% depending on where you live, which is why a headline salary rarely matches what you can spend.
A common rule of thumb caps housing costs near 28% of gross income and total debt near 36%, but the real limits are your deposit, the interest rate and how stable your income is. Affordability is about the monthly payment you can sustain — not the largest loan a lender will approve.
ROI is the total percentage gain over the whole period; annualised return (CAGR) spreads that gain evenly across each year. A 50% ROI sounds great until you learn it took ten years — about 4% a year. Always annualise before comparing investments held for different lengths of time.
Markup measures profit against cost; margin measures the same profit against the selling price. Something that costs 100 and sells for 150 carries a 50% markup but only a 33% margin. Mixing the two up is one of the most common — and most expensive — pricing mistakes.
Investment
Einstein probably never said it, but the underlying math has been the most-broken promise of personal finance for a hundred years.
Mortgage
“Renting is throwing money away” is the most expensive myth in personal finance. The honest comparison turns on opportunity cost, transaction fees, and how long you actually stay put.
Valuation
Discounted cash flow is the most teach-able valuation method — and one of the easiest to manipulate.
All calculations use standard financial formulas (ANSI/ISO conventions where applicable). Time-value-of-money tools such as compound interest, EMI, SIP and annuities default to monthly compounding unless another frequency is set, and growth, contribution, inflation and tax inputs are applied in that order so nominal and inflation-adjusted figures stay consistent. Intermediate results are carried at full precision and rounded only for display — percentages to two decimal places, money amounts to the nearest unit — so chained steps never accumulate rounding error. Every calculator shows the exact formula it uses and the assumptions behind it. CrunchCalcs provides educational tools; nothing here constitutes investment, tax, or financial advice.
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