Currency Conversion — Spot Rates vs What Banks Actually Charge You
7 min read
What a mid-market rate is, how banks add their spread, and a worked example comparing the real cost across providers.
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Articles about the math behind everyday calculations.
Loan Amortization — How Each Payment Breaks Down
6 min read
Why your early mortgage payments are mostly interest, how to read an amortization table, and when an extra payment per year makes a real difference.
Compound Interest — the 8th Wonder of the World, Explained
5 min read
The formula, a worked example, the Rule of 72, and why starting early matters more than starting big.
Unit Conversions Every Traveler Needs to Know
5 min read
Miles to km, Fahrenheit to Celsius, gallons to liters — quick mental math tricks for the conversions that trip people up abroad.
How to Calculate a Fair Tip (Country by Country)
6 min read
Tipping norms vary wildly around the world. The math behind splitting, rounding, and figuring out what percentage to leave.
How to Calculate Age in Years, Months, and Days
6 min read
Age calculation is trickier than subtracting years. Leap years, month length variation, the Korean age system, and the Feb 29 edge case.
What BMI Actually Measures (and What It Doesn't)
6 min read
BMI was invented in the 1830s as a population-level statistic. Here's why it stuck around, what it can tell you, and when you should ignore it.