Guides
The math behind everyday numbers, explained in plain English, with worked examples, sources, and a free tool to try it yourself.
What Is a Good Debt-to-Income Ratio? Thresholds, Examples and How to Lower It
What is a good debt-to-income ratio? Lower is better; 36% or less is comfortable for most lenders, and mortgage limits range from 43% to 50% of gross income.
Updated Oct 24, 2026 · 5 min read💰 Money & investingRoth IRA Income Limits 2026: Phase-Out Ranges, Contribution Limits and Examples
Roth IRA income limits for 2026: the $7,500 limit phases out at $153,000–$168,000 MAGI for single filers and $242,000–$252,000 for joint filers.
Updated Oct 24, 2026 · 5 min read💰 Money & investingRMD Table 2026: IRS Uniform Lifetime Table and How to Calculate Your RMD
The 2026 RMD table: IRS Uniform Lifetime Table distribution periods by age, plus the formula (prior Dec. 31 balance ÷ factor), deadlines and penalties.
Updated Oct 24, 2026 · 5 min read➗ MathHow to Find Standard Deviation (Sample and Population, Step by Step)
How to find standard deviation: subtract the mean from each value, square, add, divide by n (population) or n − 1 (sample), then take the square root.
Updated Oct 24, 2026 · 5 min read🗂️ Images & PDFsHow to Convert HEIC to JPG (iPhone, Mac, Windows and Browser)
How to convert HEIC to JPG on iPhone, Mac, Windows or in a browser, plus what a HEIC file is, why it won't open everywhere and how to avoid quality loss.
Updated Oct 24, 2026 · 5 min read➗ MathHow to Convert Celsius to Fahrenheit (Formula, Shortcut and Chart)
How to convert Celsius to Fahrenheit: multiply by 9/5 (1.8) and add 32. Includes the reverse formula, a mental shortcut with its error, and a conversion chart.
Updated Oct 24, 2026 · 5 min read💪 Health & fitnessHow to Calculate Macros (Step-by-Step With a Worked Example)
How to calculate macros: estimate BMR with Mifflin-St Jeor, multiply by activity for TDEE, set a calorie target, then split it into grams at 4, 4 and 9 kcal.
Updated Oct 24, 2026 · 5 min read⏱️ Time & workHow to Calculate Hourly Rate From Salary (Formula and Table)
How to calculate hourly rate from salary: divide annual pay by hours worked per year (2,080 for full time). Includes a salary table, reverse formula and PTO.
Updated Oct 24, 2026 · 5 min read🎓 School & gradesHow to Calculate GPA (Weighted and Unweighted, With Examples)
How to calculate GPA: convert each grade to points, multiply by credit hours, add the quality points, and divide by total credits. Weighted examples included.
Updated Oct 24, 2026 · 5 min read🎓 School & gradesHow to Calculate Your Final Grade (and the Score You Need on the Final)
How to calculate a final grade: multiply each category score by its weight and add them. Then use a formula to find the exam score needed to hit a target grade.
Updated Oct 24, 2026 · 5 min read💪 Health & fitnessHow to Calculate Body Fat Percentage (Navy Method and Other Ways)
How to calculate body fat percentage with the U.S. Navy tape method, step by step with a worked example, plus how DEXA, skinfolds and BIA compare.
Updated Oct 24, 2026 · 6 min read💰 Money & investingCD vs High-Yield Savings: Which Earns More and When Each Makes Sense
CD vs high yield savings: a CD locks a fixed rate for a set term with early withdrawal penalties; high-yield savings stays flexible at a variable rate.
Updated Oct 24, 2026 · 5 min read