In-depth guides on personal finance, federal retirement, health, and more. Written to help you understand the math behind our calculators and make smarter decisions.
Health & FitnessWaist to hip ratio chart with WHO thresholds: below 0.85 for women and 0.90 for men avoids the abdominal obesity cutoff. How to measure and what your ratio means.
ConstructionHow much salt to add to a pool for first fill and top-ups, why salt levels drop, what causes false low-salt warnings, and how to avoid overshooting 3,200 ppm.
Health & FitnessEpley, Brzycki, Lander, and Lombardi 1RM formulas compared by rep range. Which is most accurate, when they diverge, and how to get the best estimate.
FinanceHECM loan: FHA-insured reverse mortgage rules, lending limit, eligibility requirements, six payout options, and upfront MIP costs explained.
ConstructionPool volume in gallons: rectangular, round, and oval formulas. Average depth calculation, chemical dosing per 10,000 gallons, and pump turnover rate.
GeneralRecipe conversion: scale factor = desired servings ÷ original servings. Adjust ingredients, handle spices and leaveners, resize pans, and plan batch cooking.
MathMidpoint formula: M = ((x₁+x₂)/2, (y₁+y₂)/2). How to find the midpoint, distance, and slope for any two coordinate pairs with worked examples and geometry applications.
PayrollIowa paycheck tax at flat 3.8%, Tennessee and New Hampshire take zero from wages, New Mexico progressive brackets up to 5.9%. Take-home at $50K, $75K, $100K.
Health & FitnessToddler weight and height percentile chart for ages 2 to 5: WHO reference values by sex, how growth changes after 24 months, and what to track.
Health & FitnessWhat does 99th percentile mean: the statistical definition, what it looks like in test scores, height, IQ, and how to interpret any percentile rank.
Health & FitnessEFW percentile in pregnancy: how estimated fetal weight is calculated from biometry measurements, and what low or high percentiles mean clinically.
FinanceHurdle rate vs IRR: how return thresholds are set, the accept/reject decision rule, and where IRR above the hurdle rate can still mislead.
FinanceWhat is a good 401k match: average employer rates by industry, how to compare formulas that look different, and what top companies offer.
FinanceSafe harbor 401k match: three contribution formulas, immediate vesting rules, and why employers choose it over standard matching.
FinanceHow 401k employer matching works: dollar-for-dollar vs percentage formulas, vesting schedules, and whether employer match counts toward your limit.
FinanceHow to calculate IRR on the TI-84 Plus using the irr( function: cash flow entry, frequency argument, and ERR:NO SIGN CHG fixes.
FinanceReal estate IRR: how to build the cash flow series, levered vs unlevered difference, deal benchmarks, and what distorts the number.
FinanceCanadian silver coin melt value: 80% pre-1968 dimes, quarters, halves, 1967 transition, Silver Maple Leaf purity, formula, and reference table.
Health & FitnessInBody scan vs DEXA scan: how each measures body fat, where results diverge, and which test to choose based on your goal and budget.
Health & FitnessFFMI calculator: fat-free mass index formula, score chart by training level, the natural limit of 25, and how FFMI compares to BMI for body composition.
FinanceDSCR loan minimum requirements by lender type, how income and debt are calculated, and how DSCR loans differ from conventional investment property loans.
Health & FitnessAnion gap normal range is 8 to 12 mEq/L. Albumin correction, MUDPILES causes of high anion gap, delta ratio formula, and normal gap acidosis explained.
Health & FitnessMean blood glucose to A1C: the ADAG formula, GMI equation, reference table from 70 to 300 mg/dL, and why your CGM average and lab A1C sometimes don't match.
Health & FitnessCorrected calcium adjusts for albumin using the Payne formula. This guide covers when the correction is reliable and when to order ionized calcium instead.
Health & FitnessThe 50th percentile is the WHO median reference value for age and sex. See monthly weight and length tables for boys and girls and learn how to read a trajectory.
Health & Fitness3rd percentile means a baby's measurement is near the lower tail of a same-age, same-sex growth standard. What the number shows and what context it cannot replace.
FinanceSilver refineries pay 70-95% of spot depending on silver type and buyer. How the dealer spread works for 925, 999, and coin silver, and how to compare offers.
FinanceFERS sick leave converts at 2,087 hours per year. Dollar value by High-3 salary, the 1.1% multiplier at 62, and what sick leave cannot do for retirement eligibility.
Health & FitnessGMI (Glucose Management Indicator) formula explained: 3.31 + 0.02392 × mean glucose. Reference table in mg/dL and mmol/L, and when GMI differs from your lab A1C.
Health & FitnessSpirits ABV chart: most liquor at 40% (80 proof), overproof rum to 75.5%, barrel bourbon to 65%. Why 40% became the standard and what changes above 50% ABV.
Health & FitnessWine ABV ranges from 5.5% Moscato to 17% Zinfandel. Full chart by grape and region, how fermentation controls alcohol percentage, and what the label tolerance allows.
Health & FitnessABV stands for alcohol by volume, the universal standard for measuring alcohol strength. What the percentage means, legal tolerances, and ranges by drink type.
Health & FitnessBeer ABV ranges from 2.4% ultra-light to 15% imperial stout. Full chart by style with verified examples, standard drink math, and why craft brewing expanded the range.
PayrollIllinois final paycheck: IWPCA requires payment by next regular payday. 2% monthly late penalty, PTO payout rules, and steps if your employer withholds.
PayrollIllinois hourly paycheck after taxes: flat 4.95% state rate, overtime rules, and take-home at $15 to $30 per hour for weekly and biweekly pay periods.
FinanceIRR in Excel uses three functions depending on cash flow timing. When to use =IRR, =XIRR, and =MIRR, with syntax, worked examples, and #NUM! fixes.
FinanceIRR, ROI, and equity multiple measure different things. Which to use for real estate and private equity, and when the three metrics conflict.
FinancePE funds report gross IRR; LPs receive net. How the gap is calculated, why funds show negative IRR early, and the three metrics that tell the full story.
FinanceIRR and NPV often agree, but four scenarios cause them to conflict. Which to trust for scale comparisons, mutually exclusive projects, and capital allocation.
FinanceA good IRR means different things for real estate, private equity, and stocks. Hurdle rates, benchmarks by strategy, and when a high IRR misleads.
EducationLaw school scholarship negotiation works when you hold a competing offer. Timing, what to say, and where schools have the most flexibility to move.
EducationLaw school scholarships for women and minorities come from two sources: school merit aid and external programs. How to find both and what qualifies.
EducationThe law schools that give the most scholarships are not the top-ranked ones. Which rank tiers offer the most merit aid and how to find your targets.
EducationFull ride law school scholarships: which school tiers offer full tuition, LSAT scores that qualify, and when a full ride beats a higher-ranked school.
EducationLaw school scholarships come down to LSAT and GPA vs school medians. How thresholds work, the renewal trap, and where full scholarships actually come from.
PayrollCalifornia hourly paycheck calculator: how daily overtime after 8 hours works, double time after 12, SDI on hourly wages, and take-home at $18, $25, and $35/hr.
PayrollCalifornia paycheck laws: how often employers must pay, what every pay stub requires, legal vs illegal deductions, and penalties for late regular paychecks under Labor Code 210.
PayrollCalifornia final paycheck law: termination means same-day pay, resignation with notice means last day, without notice means 72 hours. Labor Code 203 penalties explained.
PayrollCalifornia paycheck tax breakdown: CA income tax 1%–13.3%, SDI 1.1% no cap, federal withholding, and take-home at $50K, $75K, and $100K for single filers.
FinanceCalculate scrap value of sterling silver jewelry and flatware. Covers pennyweight, weighing rings and chains, flatware patterns, and what dealers offer.
FinanceGold to silver ratio calculator: the formula, historical range from 1900 to today, how investors use it to time metal swaps, and why it expanded after 1971.
FinanceSilver-plated items have near-zero scrap value. How to identify plate vs solid sterling, what EPNS hallmarks mean, and when antique premiums apply.
FinanceSilver coin melt value calculator for US dimes, quarters, halves, and dollars. Silver content by coin type, date, formula, and dealer payout rates.
Health & Fitness99th percentile means heavier than 99% of the same-age reference distribution. What high and low weight-for-age percentiles do—and do not—show.
Health & FitnessBaby percentile during pregnancy compares estimated fetal size at the same gestational age. How EFW is calculated and what low or high results do and do not show.
Health & FitnessBaby weight percentile chart with WHO reference values from birth to 24 months. Selected tables for boys and girls, plus the WHO LMS calculation method.
PayrollOhio hourly paycheck: 0% on first $26,050, then 2.75%. How overtime, SDIT, and city tax affect hourly workers' take-home pay at $15 to $30/hr.
Health & FitnessBaby percentile compares your baby's weight or length to WHO reference babies the same age and sex. What the number means, how it's calculated, and what to watch.
PayrollIllinois income tax: constitutionally fixed 4.95% flat rate, full pension and Social Security exemption. Take-home pay at $50K, $75K, $100K for 2025.
PayrollNebraska income tax: 4-bracket system with a top rate dropping to 3.99% by 2027. Social Security now fully exempt. Take-home at $50K, $75K, $100K.
PayrollMinnesota income tax: 4 brackets from 5.35% to 9.85%, no local tax anywhere in the state. Take-home pay at $50K, $75K, and $100K for 2025.
PayrollUtah income tax: flat 4.55% rate with a personal exemption credit that reduces your bill directly. Take-home pay at $50K, $75K, and $100K for 2025.
PayrollOhio city income tax guide: rates for Columbus, Cleveland, Cincinnati, Toledo. How the resident credit works when you live in one city and work in another.
PayrollOhio SDIT explained: 210+ districts levy 0.5% to 2.5% based on where you live. Traditional vs. Earned Income types, top district rates, and what to do if not withheld.
FinanceFERS supplement calculator guide: who qualifies, how to calculate the amount, earned income test, sick leave credit, and when the supplement stops at 62.
PayrollNY paycheck calculator guide: NJ graduated rates, Indiana county taxes, Michigan city taxes, and NYC city tax. Take-home pay at $55K and $85K.
PayrollSouth Carolina 2026: simplified 1.99% and 5.21% rates replace the old six-bracket system. Military exemption, SS exemption, and take-home pay at $50K to $100K.
PayrollWisconsin paycheck tax: 3.5% to 7.65% brackets with a sliding standard deduction that phases out by $106K income. Take-home pay at $50K to $100K.
PayrollMaryland paycheck tax: 4.75% to 6.5% state rates plus county income tax up to 3.30%. All 23 county rates and take-home pay at $60K to $120K.
FinanceSilver bar calculator for 1 oz, 10 oz, and 100 oz bullion. Covers silver bullion value, bar premiums, rounds vs bars, and live spot price calculation.
Finance925 silver price per gram today, plus per-gram values for 999, 900, 835, and 800 grade silver at current spot. Formula, quick-reference table, and live calculator.
PayrollAlaska has no state income tax. Hawaii's top rate reaches 11%. Idaho went flat at 5.8% in 2023. Kentucky cut to 4.0%. Take-home pay at $50K, $75K, and $100K compared.
FinanceOld silver rate is today's spot price adjusted for purity and dealer margin. How to calculate old silver value per gram, why old rates differ from new silver, and what affects the price in your city.
PayrollMassachusetts paycheck tax guide: 5% flat state income tax, PFML withholding explained. Take-home pay at $60K, $80K, and $120K for 2025-26.
PayrollOhio paycheck tax guide: 0% on first $26,050, 2.75% to 3.125% for 2025 taxes. SDIT and city tax explained. Take-home pay at $50K-$100K.
FinanceExact keystroke sequences for HP 12C and BA II Plus, plus XIRR in Excel. Worked investment example: enter cash flows, press IRR, read result. Under 5 minutes.
MathAcceleration calculator: find acceleration from velocity change and time, or use any of the 3 kinematic equations. All units supported. Free, no signup.
Health & FitnessA1C calculator: convert average blood glucose or GMI to estimated A1C using the ADA ADAG formula. mg/dL and mmol/L both supported. Free, no signup.
MathPower rule, polynomial, exponential, and log antiderivatives with worked examples. How to find any antiderivative and verify the result.
FinanceProrated rent = rent ÷ days in month × days occupied. Covers move-in, move-out, and mid-month examples, daily-rate method, and when landlords use a 30-day month.
Finance2026 Roth IRA limits: $7,000 ($8,000 if 50+). Phase-out begins at $150k single, $236k married. Calculate your exact allowed contribution. No signup.
FinanceCap rate = NOI divided by property value. Learn the formula, see examples by property type, and find out what cap rate benchmarks apply to your investment.
FinancePre-1965 US coins hold 90% silver. Calculate junk silver value by weight, coin type, and grade. Covers dimes, quarters, and 800-grade European silver.
MathPartial derivatives measure how a function changes in one direction while others are fixed. Rules, worked examples, gradient, and applications.
MathA determinant shows if a matrix has an inverse and if a linear system has a unique solution. Step-by-step 2x2 and 3x3 methods with examples.
FinanceCommercial mortgage payments depend on rate, amortization, and balloon term. DSCR determines approval. Worked examples with real numbers.
Health & FitnessTotal calcium is unreliable with low albumin. The Payne correction formula adjusts for protein binding. When to use it and when ionized calcium is better.
FinanceIRR is the discount rate that makes an investment's NPV equal zero. Formula, worked examples, MIRR correction, and when IRR misleads.
ConstructionSquare footage is length times width for simple rooms. L-shapes and bay windows change the math. Exact method for rooms, floors, and whole houses.
FinanceCap rate measures income yield today. IRR captures total return with timing. How to calculate both and when each applies to a real estate deal.
FinanceCoast FIRE needs a larger portfolio but no part-time income. Barista FIRE gets you there sooner with less saved. Compare numbers and timelines.
Health & FitnessIn the US, proof is ABV doubled. A 40% spirit is 80 proof. Conversion table, formulas, and how the old UK proof system set 100 proof at 57% ABV.
Health & FitnessBrix from a refractometer converts to SG and potential ABV. Includes a Brix-to-SG table, the ABV formula, and correction for post-fermentation readings.
Health & FitnessCalculate ABV from original and final gravity using the standard homebrewing formula. Worked examples for beer, wine, and cider. No signup.
Health & FitnessHow to use a hydrometer to take gravity readings, apply temperature corrections, and calculate ABV from homebrew measurements. No signup.
FinanceScrap silver value = weight (troy oz) × purity % × spot price. Covers 925, 900, and coin silver. Purity hallmark guide and current dealer spread included.
FinanceSilver is priced in troy ounces, not standard ounces. Convert to grams, calculate value by purity and weight, and understand live spot price.
MathComplete trig antiderivatives reference: sin, cos, tan, cot, sec, csc, plus 1/x, ln x, and e^x. Derivations, worked examples, and quick reference table.
Health & FitnessLearn how to calculate your menstrual cycle length, when a period is late vs missed, and what affects period calculator accuracy. Includes manual formula.
Health & FitnessHow to calculate chronological age by hand, in years and months, for Pearson assessments, speech therapy, and prematurity adjustment. Free guide.
Health & FitnessStarbucks nutrition guide covering latte calories, Frappuccino calories, low calorie options, syrup nutrition, and custom order calorie calculation.
FinanceHow to calculate your FERS retirement annuity, High-3 salary, sick leave credit, FERS supplement, and early retirement reduction rules. Step-by-step.
FinanceHow to calculate your Coast FIRE number with worked examples, a reference table by age, and adjustments for Social Security and pension income.
FinanceNo law sets an equity floor for reverse mortgages, but the math creates one. How requirements work by age, home value, and rate, with real examples.
FinanceHow to calculate a reverse mortgage: principal limit factor, upfront costs, payout options, and worked examples for different ages and home values.