Blog
Deep dives into the data and formulas behind everyday calculators. Every post is written by someone who has used the calculator for real decisions, buying a house, wiring a circuit, cutting body fat, sizing a solar array.
Finance
Reading Your Paycheck: What Every Deduction Actually Means in 2026
Federal income tax, FICA, Medicare surtax, state tax, 401(k), HSA, FSA, health premiums, garnishments, line by line, with the exact 2026 rates and thresholds applied to real sample paychecks.
Health
TDEE: The Only Calorie Number That Actually Drives Weight Change
BMR tells you the baseline. Calorie intake tells you the input. TDEE is the number that decides whether you lose, maintain, or gain, and it is the one most people miscalculate.
Health
BMI vs. Body Fat Percentage: Which Number Actually Measures Health
BMI is free and fast. Body fat percentage is more accurate. Waist-to-hip ratio predicts cardiovascular risk better than either. Here is when to use which, and what the CDC and WHO actually recommend.
Finance
Compound Interest, Explained in the Math Your Calculator Actually Uses
The formula A = P(1 + r/n)^(nt) is one of the most useful equations in personal finance. Here is how each variable actually behaves, and why compounding frequency matters less than you think.
Clean Energy
Solar Payback Period Math: What Installers Do Not Tell You
A 6-year payback is possible in Arizona. In Seattle, it is 14. The difference comes down to three variables, peak sun hours, retail electricity rate, and the 30% federal tax credit, that installers rarely show together.
Business
The True Cost of Hiring an Employee: A Full Line-Item Breakdown
A $80,000 salary costs roughly $108,000 fully loaded, and that is before you account for recruiting, equipment, and the onboarding productivity gap. Here is every cost line, with current 2025 rates.
Finance
Why the 28/36 Rule Fails Most Homebuyers in 2025
The classic mortgage-affordability rule was built for a world without student loans, rising property taxes, or $8,000 HOA dues. Here is a better framework, and the DTI math lenders actually use.
Construction
How to Calculate Concrete Cubic Yards Without Ordering Twice
Every DIY concrete pour has the same failure mode: underordering. Here is the actual math, with the waste factors, short-load fees, and the 3% rule nobody tells you.