Calculator Guides
Deep dives into the math behind our calculators. Written by the CalcNow Editorial Team against primary sources (US Treasury, CDC, BLS, Federal Reserve, BIPM, WHO) and updated as guidelines change.
- Health
BMI vs BMR vs TDEE: Which Should You Use to Track Your Health?
Three metrics, one body — why they get confused. A decision tree for when to use each one, with Mifflin-St Jeor and WHO references.
·9 min read·CalcNow Editorial Team - Finance
Understanding Compound Interest: How Your Money Actually Grows
The formula, compounding frequency, the Rule of 72, and why starting early matters more than rate. Also covers the dark side (credit card debt).
·10 min read·CalcNow Editorial Team - Conversion
Imperial vs Metric: A Practical Guide for International Workflows
Why only three countries still use Imperial. Length, weight, volume, and temperature — plus the US vs UK gallon trap and the Mars Climate Orbiter disaster.
·9 min read·CalcNow Editorial Team - Finance
Rent vs Buy: The Real Math Behind Homeownership
The "throwing money away on rent" myth, true cost of buying (~60% price tag), the 5-year rule, and regional differences (Dallas vs San Francisco).
·10 min read·CalcNow Editorial Team - Finance
How to Budget: The 50/30/20 Rule (and When It Doesn't Work)
Elizabeth Warren's 2005 framework broken down. Needs, wants, savings — and when this rule breaks down (high-cost cities, high debt, low income).
·9 min read·CalcNow Editorial Team