Math & Everyday
How to Calculate a Tip (and Split the Bill)
A fast mental method for 15%, 18%, and 20% tips — plus how to split the total across the table.
Guides
Calculator guides & articles
The reasoning behind the numbers — how to estimate a project, plan your taxes, read your health metrics, and make everyday math easy.
Health
How Many Calories Should You Eat to Lose Weight?
Find your maintenance calories, then subtract a sensible deficit. A 500-calorie daily cut is about one pound a week.
Finance
Roth vs. Traditional: Which Retirement Account Wins?
It comes down to one question: will your tax rate be higher now or in retirement? Here's how to decide.
Construction
Does a New Roof Pay Off at Resale? Roof Replacement ROI
A new asphalt roof recoups about 60% of its cost at resale — but the bigger value is that it often lets the home sell at all.
Construction
Does New Siding Add Home Value? Siding ROI Explained
New siding is one of the highest-return exterior projects — fiber cement recoups roughly 80–88% of its cost at resale.
Construction
Does a New Deck Add Home Value? Deck ROI in 2026
A wood deck recoups about 50–83% of its cost at resale. Here's how material, size, and your market change the return.
Construction
Metal Roof vs. Asphalt Shingles: Which Is Worth It?
Metal costs about twice as much upfront but lasts two to three times longer. Here's how to decide based on how long you'll stay.
Construction
Are Gutter Guards Worth It? Cost vs. Payback in 2026
Gutter guards run about $1,000–$3,500 installed. Here's how to weigh that against years of cleaning bills and water-damage risk.
Math & Everyday
How to Calculate Exact Age in Years, Months, and Days
Counting age precisely means handling different month lengths and leap years. Here's the method behind it.
Math & Everyday
How to Calculate Percentages (3 Common Cases)
Find a percentage of a number, figure out what percent one number is of another, or calculate percent change.
Health
How to Calculate Your Daily Calorie Needs (TDEE)
Your TDEE is the calories you burn in a day. Here's how the Mifflin-St Jeor equation and an activity factor estimate it.
Health
BMI vs. Body Fat Percentage: Which Should You Track?
BMI is a quick screen from height and weight; body fat percentage measures composition. Here's when each is useful.
Finance
How Self-Employment Tax Works for Freelancers
Self-employment tax is the 15.3% Social Security and Medicare freelancers pay on their own. Here's how it's calculated.
Finance
Marginal vs. Effective Tax Rate: What's the Difference?
Your marginal rate applies to your next dollar; your effective rate is what you actually pay overall. Here's why they differ.
Construction
Concrete Basics: Cubic Yards, Bags, and Waste
Concrete is sold by the cubic yard (27 cubic feet). Here's how to size a pour and decide between bags and ready-mix.
Construction
How Many Roofing Squares Is Your Roof?
A roofing square is 100 square feet. Here's how to convert your roof's footprint and pitch into squares and shingle bundles.