Guides & explainers
Short, practical articles that pair with our calculators.
How to Calculate Gear Ratio: Formulas, RPM, and Gearbox Math
Master gear ratio calculations, output RPM conversions, torque leverage, and multi-stage gearbox speed formulas with clear worked examples.
6 min read
How to Calculate BMI (and What It Actually Tells You)
The BMI formula, worked examples, and where the number falls short.
4 min read
What Is Compound Interest?
Why compounding frequency matters more than most people expect.
5 min read
How GPA Is Calculated
Credit-weighted averages explained with a worked transcript.
3 min read
The Practical Mortgage Guide
How amortisation splits your payment between interest and principal.
6 min read
GST Explained: Adding vs Removing Tax
Inclusive and exclusive pricing, and the mistake most people make.
4 min read
A Complete Loan Calculator Guide
Tenure, rate and principal — which lever actually saves money.
5 min read
EMI vs Total Interest: The Number Lenders Don't Advertise
Why two loans with the same instalment can differ by hundreds of thousands in interest, and how to read an amortisation schedule properly.
5 min read
The Car Loan Trap: When Your Loan Outlasts Your Car's Value
Long terms make cars feel affordable and quietly leave buyers owing more than the vehicle is worth. Here's the arithmetic behind negative equity.
4 min read
Why Credit Card Minimum Payments Never Seem to End
The minimum payment is designed to shrink as your balance shrinks. That single feature is what turns a modest balance into a decade of payments.
4 min read
SIP Maths: Why the Last Five Years Do the Heavy Lifting
Each monthly instalment compounds for a different length of time. Understanding that staircase explains why quitting a SIP early costs so much.
5 min read
CAGR vs Average Return: The Mistake That Flatters Every Portfolio
Averaging yearly percentages makes volatile investments look better than they were. Geometric growth is the only honest way to combine returns.
4 min read
ROI Is a Useful Number That Hides Two Important Things
Return on investment ignores time and risk. Both omissions can turn a bad decision into a persuasive slide.
4 min read
Your Retirement Number Is Probably in the Wrong Currency
A million in 2050 is not a million today. Here's how to keep a retirement projection honest about purchasing power.
5 min read
Flat rate vs reducing balance: why an 8% car loan costs 15%
Two loans, the same headline rate, nearly double the real cost. Here is the arithmetic dealers rely on you not doing.
6 min
What a 1% fee really costs over thirty years
It sounds like a rounding error. Run the compounding and it is a fifth of your portfolio.
5 min
Nominal vs real: the return that actually buys things
Your account balance grew 7%. Your purchasing power may not have grown at all. Here is how to tell.
6 min
The price-cut trap: why a 10% discount needs 50% more sales
Discounting feels like a growth lever. On thin margins it is a volume treadmill you cannot run fast enough.
5 min
Marginal vs effective tax: why a raise never costs you money
Entering a new tax bracket does not tax your whole income at the new rate. Here is the bracket arithmetic, worked out.
5 min
The 28/36 rule: how lenders decide what you can borrow
Your credit score gets the attention, but debt-to-income is what usually decides the answer.
6 min
Body fat vs BMI: why the scale misreads a muscular body
Two people, same height, same weight, completely different health profiles. BMI cannot tell them apart.
6 min
Why your calorie target stops working after two months
Nothing changed except your body. That is precisely the problem, and there are three fixes.
6 min
Set protein first: the macro order that actually works
Percentage splits quietly starve you of protein exactly when you need it most. Here is the better sequence.
5 min
Degrees vs Radians: The Silent Trig Calculator Bug
The same sin() call gives two different answers depending on one toggle. Here's how to always know which one you're getting.
4 min
The Discriminant: Knowing the Answer's Shape Before You Solve
b² − 4ac tells you whether a quadratic has two real roots, one, or none — before you finish the formula.
4 min
Ohm's Law: The One Formula Electronics Keeps Coming Back To
V = I × R looks trivial until you realise it's the answer to nearly every 'why isn't this circuit working' question.
4 min
Why 45 Degrees Isn't Always the 'Best' Launch Angle
Physics says 45° maximises range — but only under an assumption that almost never holds in the real world.
4 min
Escape Velocity: Why Mass Doesn't Matter (But Direction Sort Of Does)
A feather and a rocket need exactly the same escape velocity from Earth — here's the counterintuitive reason why.
4 min
Why Computers 'Speak' in Hex, Not Decimal
Binary is what computers actually use — hex is the readable shorthand humans use to talk about it. Here's why base 16 specifically won.
4 min
Why 'Add 30 Days' Never Lands Where You Expect
Thirty days from now isn't 'next month, same date' — and the gap between those two answers can matter more than people expect.
3 min