CalcDesk Guides
Plain-English explainers behind our most-used tools — how the formulas work, where the common estimates break down, and how to read results like a pro.
All nine guides
How Mortgage Payments Are Calculated
The exact amortisation formula behind your monthly payment, how interest and principal split over time, and which costs a payment estimate leaves out.
Read guide →What BMI Gets Wrong (and When to Ignore It)
BMI is a screening tool built for populations, not people. Where it mislabels athletes, elderly, ethnic groups — and the measurements that do better.
Read guide →TDEE Explained: What Your Body Actually Burns in a Day
BMR vs TDEE, how the Mifflin-St Jeor equation works, choosing an activity multiplier honestly, and how to use the number for losing or gaining weight.
Read guide →Discount Math: Percentages, Stacking, and Reading a Sale Correctly
How to compute any discount, why stacked percentages multiply instead of add, and how retailers use percentage framing to sell more.
Read guide →How Much Water Should You Actually Drink?
Where the 8-glasses myth came from, what weight-based estimates really say, when coffee counts, and the simple daily signals that beat any formula.
Read guide →ROI vs Annualised Return: Comparing Investments Fairly
Why raw ROI hides time, how annualising works, what a good ROI looks like by asset class, and the costs most people forget to subtract.
Read guide →How Loan Interest Works (and How to Pay Less of It)
Flat vs reducing-balance interest, why early payments are mostly interest, and the four levers that cut the total interest you pay.
Read guide →How Much House Can You Actually Afford?
The 28/36 rule, what lenders look at, the hidden costs beyond the mortgage payment, and how to stress-test a purchase before committing.
Read guide →Percentages in Everyday Life: A Field Guide
Tipping, taxes, interest, discounts, statistics and battery bars — the handful of percentage patterns that cover almost everything you meet.
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