I Want My Money Back

Most of the last stretch of work on this site hasn't been visible from the outside. No flashy new pages, no redesign - just a lot of building, reorganizing, and cleaning up in the background so the platform holds together better as it grows.

A Lot More Calculators

The calculator collection grew by a wide margin this round. Below are the new additions that haven't been called out in a previous post yet, grouped by category.

Financial

• 401(k) Calculator - Project your 401(k) balance at retirement, including employer match and optional annual raises.
• Annuity Calculator - Project the future value of an annuity's accumulation phase.
• Annuity Payout Calculator - Calculate the fixed payout an annuity can generate over a guaranteed term.
• Average Return Calculator - Compare arithmetic mean vs. geometric mean (CAGR) returns across periods.
• Boat Loan Calculator - Monthly payment, total interest, and full amortization for a boat loan.
• Budget Calculator - Compare spending against the 50/30/20 rule or your own custom split.
• Business Loan Calculator - Payment, net proceeds after fees, and total cost of a business loan.
• Canadian Mortgage Calculator - Payments using Canada's semi-annual compounding rules.
• College Cost Calculator - Project future college costs and the monthly savings needed to close the gap.
• Commission Calculator - Flat or tiered sales commission, plus On-Target-Earnings.
• Credit Card Calculator - Payoff time, total interest, and the real cost of minimum payments.
• Debt Consolidation Calculator - Compare separate debts against a single consolidation loan.
• Debt Payoff Calculator - Snowball vs. avalanche payoff strategies, side by side.
• Depreciation Calculator - Straight-line, declining balance, or sum-of-years-digits depreciation schedules.
• Discount Calculator - Stacked percent-off discounts, or work backward from a sale price.
• Estate Tax Calculator - Estimate federal estate tax against the current exemption.
• Income Tax Calculator - Federal tax liability, marginal rate, and effective rate.
• Inflation Calculator - See how inflation changes purchasing power over time.
• IRA Calculator - Project a Traditional IRA balance and this year's tax deduction.
• IRR Calculator - Internal rate of return for an investment and its cash flows.
• Loan Calculator - Monthly payment and amortization for any fixed-rate installment loan.
• Margin Calculator - Required margin and buying power for a leveraged position.
• Marriage Tax Calculator - See if filing jointly saves you money or costs you money.
• Mutual Fund Calculator - Project fund value net of expense ratio and load fees.
• Payback Period Calculator - How long it takes to recover an initial investment.
• Paycheck Calculator - Take-home pay after taxes and pre-tax contributions.
• Pension Calculator - Estimate a defined-benefit pension payout.
• Personal Loan Calculator - Payment, net proceeds, and total interest on a personal loan.
• Retirement Calculator - How long a self-managed retirement portfolio will last.
• RMD Calculator - Required Minimum Distribution using the IRS Uniform Lifetime Table.
• ROI Calculator - Total and annualized return on investment.
• Roth IRA Calculator - Project a tax-free Roth IRA balance at retirement.
• Sales Tax Calculator - Add tax to a price, or back it out of a total.
• Social Security Calculator - Estimate your benefit and how claiming age changes it.
• Student Loan Calculator - Payment, interest, and payoff timeline, including grace-period capitalization.
• UK Mortgage Calculator - UK mortgage payments plus Stamp Duty Land Tax.
• VAT Calculator - Add VAT to a net price, or back it out of a gross price.

Health

• Army Body Fat Calculator - The U.S. Army tape-test method compared against Army standards.
• BAC Calculator - Estimate blood alcohol concentration using the Widmark formula.
• BMR Calculator - Basal Metabolic Rate via Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle.
• Body Surface Area Calculator - BSA from the Mosteller and DuBois formulas.
• Body Type Calculator - Estimate ectomorph, mesomorph, or endomorph frame size.
• Calories Burned Calculator - Calories burned during exercise using MET values.
• Carbohydrate Calculator - Recommended daily carb intake from your calorie needs.
• Conception Calculator - Estimate a likely conception date range.
• Due Date Calculator - Estimated due date from last period, conception, or ultrasound.
• Fat Intake Calculator - Recommended daily fat intake from your calorie needs.
• GFR Calculator - Kidney function estimate via the race-free CKD-EPI 2021 equation.
• Healthy Weight Calculator - Healthy weight range using the WHO BMI band.
• Lean Body Mass Calculator - Fat-free mass via the Boer, James, and Hume formulas.
• Macro Calculator - Daily protein, carb, and fat targets from your calorie needs.
• One Rep Max Calculator - Estimate 1RM using the Epley and Brzycki formulas.
• Overweight Calculator - Excess weight above the healthy BMI ceiling, plus a loss timeline.
• Ovulation Calculator - Predict ovulation day and fertile window.
• Period Calculator - Predict upcoming menstrual period dates.
• Pregnancy Calculator - Due date, gestational age, and trimester milestones.
• Pregnancy Weight Gain Calculator - Recommended weight gain range using IOM guidelines.
• Protein Calculator - Recommended daily protein intake from weight and activity level.
• Target Heart Rate Calculator - Training zone using the Karvonen method.
• TDEE Calculator - Total Daily Energy Expenditure from BMR and activity level.

Math

• Area Calculator - Quick area formulas for 7 common 2D shapes.
• Average Calculator - Mean, sum, count, min, and max of a list of numbers.
• Basic Calculator - Full on-screen keypad with memory and calculation history.
• Big Number Calculator - Arbitrary-precision arithmetic beyond JavaScript's safe-integer range.
• Binary Calculator - Arithmetic and bitwise operations on binary numbers.
• Circle Calculator - Radius, diameter, circumference, area, arc length, and sector area.
• Confidence Interval Calculator - Confidence interval for a population mean.
• Distance Calculator - Distance and midpoint between two points in 2D or 3D.
• Exponent Calculator - Computes b^n, including decimal and negative exponents.
• Factor Calculator - Every factor and factor pair of an integer, plus prime/composite check.
• GCF Calculator - Greatest common factor with the full Euclidean algorithm shown.
• Half-Life Calculator - Solve for any variable in radioactive/exponential decay.
• Hex Calculator - Arithmetic and bitwise operations on hexadecimal numbers.
• LCM Calculator - Least common multiple with the prime factorization method shown.
• Log Calculator - Logarithms in any base, plus common log and natural log shortcuts.
• Long Division Calculator - Full step-by-step long division work grid.
• Matrix Calculator - Matrix addition, multiplication, determinant, inverse, and transpose.
• Mean, Median, Mode & Range Calculator - Core descriptive stats from a list of numbers.
• Number Sequence Calculator - nth term and sum of arithmetic or geometric sequences.
• P-value Calculator - P-value from a z-score or t-score, one- or two-tailed.
• Percent Error Calculator - Error between an experimental and theoretical value.
• Percentage Calculator - Four common percentage modes in one tool.
• Permutation and Combination Calculator - nPr and nCr with full formula breakdown.
• Prime Factorization Calculator - Breaks a number into its prime factors and exponent notation.
• Probability Calculator - Single events, AND/OR combinations, complements, and n-choose-k.
• Pythagorean Theorem Calculator - Solve for a missing leg or hypotenuse.
• Quadratic Formula Calculator - Roots, discriminant, vertex, and axis of symmetry.
• Random Number Generator - Random integers or decimals in a custom range.
• Ratio Calculator - Simplify, solve, or scale a ratio.
• Right Triangle Calculator - Every side, both acute angles, area, and perimeter.
• Root Calculator - Square roots, cube roots, and arbitrary nth roots.
• Rounding Calculator - Five rounding modes, including half-to-even.
• Sample Size Calculator - Required sample size for surveys and studies.
• Scientific Calculator - Trig, logs, powers, roots, factorial, and constants.
• Scientific Notation Calculator - Convert to/from scientific notation and do arithmetic in it.
• Slope Calculator - Slope, slope-intercept equation, distance, and midpoint.
• Standard Deviation Calculator - Population and sample standard deviation and variance.
• Statistics Calculator - All-in-one mean, median, mode, variance, quartiles, and IQR.
• Surface Area Calculator - Surface area for cubes, prisms, spheres, cylinders, and cones.
• Triangle Calculator - Solve any triangle from SSS, SAS, ASA, or AAS.
• Volume Calculator - Volume for cubes, prisms, spheres, cylinders, and cones.
• Z-score Calculator - Z-score, reverse solve for x, and percentile lookup.

Everyday, Home & Network

• Bandwidth Calculator - Transfer time from file size and connection speed, or reverse it.
• Density Calculator - Density from mass and volume, in kg/m³, g/cm³, and lb/ft³.
• Dew Point Calculator - Dew point from temperature and humidity via the Magnus formula.
• Dice Roller - Roll virtual dice, d4 to d100.
• Electricity Calculator - Energy use and running cost of any appliance.
• Fuel Cost Calculator - Fuel needed and total cost for a trip.
• Gas Mileage Calculator - MPG or L/100km, plus cost per mile.
• GDP Calculator - GDP via the expenditure approach.
• Golf Handicap Calculator - Score differential from score, course rating, and slope.
• Gravel Calculator - Gravel needed for a driveway or path.
• Heat Index Calculator - "Feels like" temperature via the NWS Rothfusz regression.
• Height Calculator - Convert between feet/inches, centimeters, and meters.
• Horsepower Calculator - Estimate horsepower from trap speed or torque and RPM.
• Mass Calculator - Convert mass across metric and imperial units.
• Mileage Calculator - Reimbursement or tax deduction using the standard mileage rate.
• Molarity Calculator - Solution molarity from solute mass, molar mass, and volume.
• Molecular Weight Calculator - Molar mass of any chemical formula.
• Mulch Calculator - Mulch needed for garden beds.
• Ohm's Law Calculator - Solve for voltage, current, resistance, or power.
• Resistor Calculator - Decode 4-band or 5-band resistor color codes.
• Roman Numeral Converter - Convert numbers to and from Roman numerals.
• Shoe Size Conversion - Convert shoe sizes across US, UK, and EU systems.
• Sleep Calculator - Best bedtime or wake time based on 90-minute sleep cycles.
• Speed Calculator - Speed in mph, km/h, m/s, and knots.
• Tip Calculator - Tip amount, total bill, and per-person split.
• Tire Size Calculator - Compare two tire sizes for diameter and speedometer accuracy.
• Voltage Drop Calculator - Voltage drop across a wire run.
• Weight Calculator - Convert weight, and see it on other planets.
• Wind Chill Calculator - "Feels like" temperature via the official NWS formula.

Reorganizing the URL Structure

Alongside all of that, I spent a chunk of time cleaning up how the site's URLs are organized. Categories and slugs are now consistently English across both languages, with a single canonical URL per page and legacy links quietly redirecting instead of creating duplicate pages. It's not something most visitors will ever notice directly, but it makes the site easier to maintain and better organized for search going forward.

The Quiet Work

None of this is glamorous. It's mostly hardening, restructuring, and filling in gaps - the kind of work that doesn't show up as a feature announcement but adds up to a more solid platform underneath. Expect the pace to stay about the same: a steady stream of new calculators, with periodic cleanup passes to keep the whole thing organized as it grows.