How to Calculate

Ten focused guides with formulas, step-by-step math, comparison tables, and direct links to the calculators that match each topic. Built for searchers who want the method first, then a tool to check their numbers.

Finance

How to Calculate a Mortgage Payment (PITI & Amortization)

Learn how to calculate mortgage payments with the standard loan formula, what PITI includes, and how to compare 15- vs 30-year loans using a free calculator.

9 min read→ Mortgage Calculator

How to Calculate Loan Payments & Total Interest

Step-by-step loan payment math: monthly payment formula, total interest, and how to compare auto and personal loans with APR.

8 min read→ Loan Calculator

How to Calculate Compound Interest (With Contributions)

Compound interest formula A = P(1+r)ⁿ, contribution schedules, and how compounding frequency changes growth—plus a free calculator.

9 min read→ Compound Interest Calculator

How to Calculate Income Tax (Marginal vs Effective)

Understand US income tax estimates: taxable income, brackets, marginal vs effective rate, and how to use a tax calculator for planning (not filing).

8 min read→ Income Tax Calculator

Health

How to Calculate BMI (Body Mass Index)

BMI formula for kg/m² and lb/in², category chart, limitations for athletes and older adults, and a free BMI calculator.

6 min read→ BMI Calculator

How to Calculate TDEE & Daily Calories

Calculate BMR, activity multiplier, and TDEE for maintenance, cut, or bulk—with protein notes and a free TDEE calculator.

8 min read→ TDEE Calculator

Math

How to Calculate Percentages (Of, Change, Reverse)

Percentage of a number, percent change, and reverse calculations—with examples for tips, discounts, and growth rates.

7 min read→ Percentage Calculator

Business

How to Calculate MRR & ARR (SaaS Metrics)

MRR and ARR formulas, logo vs revenue churn, expansion MRR, and how to normalize annual plans—free MRR calculator.

8 min read→ MRR Calculator

Blockchain

How to Calculate Ethereum Gas Fees

Gas limit × gas price in Gwei, converting to ETH and USD, and why L2 fees differ—use the free gas fee calculator.

7 min read→ Gas Fee Calculator

Science

How to Calculate Ohm's Law (V, I, R)

Ohm's law V = I × R with worked examples, power P = V × I, and when AC/complex loads need more than DC Ohm's law.

7 min read→ Ohm's Law Calculator

Side-by-side decision guides (rent vs buy, IL vs holding, APR vs APY, and more) live on Compare. More long-form articles are on the blog.