Guides & how-tos

Your salary is gross pay; your take-home is net. Follow the paycheck waterfall through pre-tax deductions, FICA, and income tax withholding to see exactly where each dollar goes and why net is often 70-80% of gross.

The "a raise bumped me into a higher bracket, so I take home less" story is a myth. Here's how marginal brackets actually work, the difference between marginal and effective rates, and the one place the fear is half-true.

The Rule of 72 estimates how long money takes to double: 72 divided by the annual rate. Here's where it's accurate, where it drifts, how to run it in reverse, and what it reveals about inflation.

BMR is the calories you burn at complete rest; TDEE is everything you burn in a day. Here's the Mifflin-St Jeor formula, the activity multiplier table, and why TDEE is the number that sets your calorie goal.

APR is the plain annual rate; APY adds compounding. Savings quote APY, loans quote APR. Here's the formula, a compounding-frequency table, and how to convert one to the other.

You don't have to attempt a true max to know it. Estimate your 1RM from a submaximal set with the Epley and Brzycki formulas, plus a % of 1RM reps chart and where the estimates lose accuracy.

CAGR is the constant annual rate that takes a value from its beginning to its ending figure. Here's the formula, a step-by-step calculation, worked examples, and why it beats a simple average return.

Waist-to-hip ratio tells you where your body stores fat, not just how much. Here are the WHO risk thresholds by sex, the right way to measure your waist and hips, and why the ratio flags risk BMI misses.

Time and a half is your regular hourly rate times 1.5, owed on hours past 40 in a workweek. Here's the step-by-step math, a rate reference table, how salaried pay works, and who actually qualifies under federal law.

MPG is just miles driven divided by gallons used. Here's the reliable pump method to measure yours, a 2026 table of what counts as good MPG by vehicle class, and how MPGe works for EVs.

One gallon covers 350-400 sq ft per coat, but most walls need two. Here's how to measure your paintable area, subtract doors and windows, and buy the right number of gallons.

A "good" VO2 max is judged against your age and sex, not against elite athletes. Here are the fair/good/excellent bands in ml/kg/min, how to estimate your score with a field test, and why it predicts how long you live.

Cost-plus, keystone, value-based, competitor, and break-even pricing, explained with worked numbers, a method comparison table, and the one formula that turns a target margin into a price.

ISPs advertise megabits (Mbps) but files download in megabytes (MB/s), and 1 byte is 8 bits. Here's the divide-by-8 rule, why overhead and Wi-Fi trim the rest, and why upload is slower.

A board foot is a unit of volume equal to 144 cubic inches. Here's the formula, why nominal size (not actual) is used, a reference table of common boards, and how hardwood is priced per board foot.

1 mg equals 1,000 mcg, so mixing up micrograms and milligrams on a supplement label is a 1,000x error. Here's the conversion table, real vitamin doses (D, B12, folate, biotin), and how IU is different.

The US Navy method estimates body fat from a few tape measurements: neck, waist, and height (women add hips). Here's the formula, how to measure correctly, how accurate it is versus DEXA, and the healthy ranges by sex.

The advertised Powerball jackpot is the annuity total, paid over 29 years; the lump sum is roughly half. Here's how each is taxed, and how to decide which to take.

Pizza is priced by diameter but you eat the area, which grows with the square of the radius. Here's why one 18-inch pizza beats two 12-inch pies, plus how to compare any deal by price per square inch.

Multiply area by depth, convert to cubic yards, then to tons. Here's the method with a worked driveway example, a coverage table for area and depth, gravel weight per yard, and 2026 costs.

Convert kilograms to pounds without a calculator: double the number and add 10%. Here's why 70 kg is 154 lb, how accurate the shortcut really is, and how to run it in reverse.

A calorie deficit is the gap between what you burn and what you eat. Here's how big to make it, why 500 a day loses about a pound a week, and how low is too low.

The billboard number is not the number you keep. See how the cash value, the 24%-vs-37% federal gap, and state tax from 0% to 10.9% shrink a jackpot to your real take-home.

Institutions don't count days like a calendar. Here's how business days, T+1 stock settlement, bank check holds, and court deadlines under FRCP Rule 6 actually count time, plus the difference between "within X days" and "by the Xth."

Multiply length by width by thickness in feet, divide by 27 for cubic yards, then add 10% waste. Here's the formula, a slab-size-to-yards-and-bags table, and when to order ready-mix instead of bagging it.

A US cup holds 8 fluid ounces (236.6 mL), but the legal cup is 240 mL, the metric cup 250 mL, and the old UK cup 284 mL. Here's the full table, a quick fl-oz-to-cups chart, and the fluid-vs-weight-ounce trap that ruins recipes.

The 10,000-steps target started as a 1965 Japanese marketing slogan. The mortality research says benefits plateau around 7,000-8,000 steps a day, and even less for older adults. Here's the evidence and a realistic goal.

$30 an hour comes to $62,400 a year at full time, or about $5,200 a month. Here's the full breakdown by pay period, what's left after 2026 taxes, and how part-time hours and unpaid time off change the number.

You get 90 days in any 180-day period across the Schengen Area, but the 180 days are a rolling window that moves with you, not a fixed reset. Here's how it really works and how to count your days.

Roof pitch is rise per 12 inches of run, written like 6:12. Here's how to read it, convert it to degrees with arctan, and use the slope factor to turn a footprint into real roof area, plus a full pitch-to-degrees table.

A US cup is always 236.6 mL of volume, but the weight inside it swings with the ingredient's density. Here's a grams-per-cup chart for flour, sugar, butter, and honey, and why baking by weight is more accurate.

Walking burns roughly 80-100 calories per mile, and a 155-pound person lands near 100. Here's the burn by body weight and pace, the simple MET formula, and why distance beats speed for total calories.

Margin and markup describe the same profit measured against two different numbers. Here's the difference in plain terms, with a conversion table and how to set a price from a target margin.