Free calculators for
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Calculate percentages and dates, compare loan payments, convert units, or explore health estimates. Choose a tool and check its units and assumptions before using the result.
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BMI Calculator
Calculate BMI from height and weight, with metric and US measurement options.
OpenAge Calculator
Find age in years, months and days from a birth date and a chosen end date.
OpenAnimal Breeding Calculator
Choose a cow, goat, horse or dog and estimate a birth window from a recorded breeding date.
OpenArea Calculator
Calculate the area of common shapes and convert the result to square units, acres or hectares.
OpenBMR Calculator
Compare resting-energy formulas and estimate daily calorie needs from body measurements and activity.
OpenBody Fat Calculator
Estimate body fat with the U.S. Navy tape method using height and body circumferences.
OpenCalorie Calculator
Estimate daily maintenance calories and weight-goal targets from age, size and activity level.
OpenCompound Interest Calculator
Project a balance from principal, interest, compounding frequency and regular contributions.
OpenConcrete Calculator
Estimate concrete volume, bags and cost for slabs, walls, columns or tubes, including waste allowance.
OpenCountdown Timer
Count down to an event in days, hours, minutes and seconds using your device clock.
OpenCow Gestation Calculator
Estimate a calving date and planning window from a cow’s breeding or insemination date.
OpenCurrency Converter
Convert an amount using a fetched or manual exchange rate, with optional spread and fee inputs.
OpenDate Difference Calculator
Count calendar days between dates or add and subtract days, weeks, months and years.
OpenDiscount Calculator
Find sale prices and savings for percent-off, fixed, stacked and buy-one-get-one style offers.
OpenDistance Calculator
Calculate straight-line or coordinate distance, or solve a speed, time and distance problem.
OpenDog Pregnancy Calculator
Estimate a whelping window from a mating date or a veterinary-timed reproductive date.
OpenEMI Calculator
Estimate monthly loan payments and view a repayment schedule from principal, rate and term.
OpenFuel Cost Calculator
Estimate fuel cost from trip distance, vehicle efficiency and fuel price, then split it per person.
OpenGoat Gestation Calculator
Estimate a kidding date and planning window from a goat’s recorded breeding date.
OpenGPA Calculator
Calculate a credit-weighted GPA on the displayed 4.0 scale or plan the grades needed for a target.
OpenHorse Gestation Calculator
Estimate a mare’s foaling date and planning window from the last recorded breeding date.
OpenIdeal Weight Calculator
Compare adult height-based weight formulas and BMI reference ranges, with clear limits.
OpenIncome Tax Calculator
Check progressive tax arithmetic with your own brackets, deductions and credits.
OpenMortgage Calculator
Estimate a mortgage payment with optional tax, insurance, fees and extra monthly payments.
OpenOvertime Pay Calculator by State
Estimate weekly gross pay from hours, hourly rate and a selected state overtime model.
OpenOvulation Calculator
Estimate a fertile window from period dates and cycle length; calendar estimates do not confirm ovulation.
OpenPaint Calculator
Estimate paint and primer quantities from wall area, coats, openings and product coverage.
OpenPercentage Calculator
Find percentages, percentage change and difference, or add and remove a percentage-based tax.
OpenPrayer Times Calculator
Calculate a prayer timetable using location, date and a selected calculation method.
OpenPregnancy Due Date Calculator
Estimate a due date from a period, conception, ultrasound or IVF transfer date.
OpenProtein Requirement Calculator
Estimate a daily protein range from weight, activity and goals, or enter your own g/kg range.
OpenRecipe Scaler
Resize ingredient quantities for a new serving count and convert kitchen units, oven temperatures or pans.
OpenRetirement Calculator
Model retirement savings and income using contribution, return, inflation and withdrawal assumptions.
OpenSalary Calculator
Convert pay between periods, model a raise or estimate income tax under the stated model.
OpenTake-Home Pay Estimate
Convert salary between pay periods and estimate pay after modeled income tax, excluding other deductions.
OpenTime Card Calculator
Add daily work hours and unpaid breaks, with optional rounding and a weekly overtime pay estimate.
OpenTime Zone Converter
Convert a date and time between time zones and compare the same moment across cities.
OpenTip Calculator
Calculate a tip and shared bill with optional tax, discounts, service charge and rounding.
OpenTrip Cost Calculator
Combine fuel, accommodation, food and other expenses into a trip budget and per-person estimate.
OpenUnit Converter
Convert length, mass, temperature, area, volume and other units, with a comparison table.
OpenVolume Calculator
Calculate volume for common 3D shapes and convert the result to litres or gallons.
OpenWaist-to-Hip Ratio Calculator
Divide waist by hip measurement and compare optional waist-to-height and BMI screening estimates.
OpenWater Intake Calculator
Convert a chosen fluid goal into cups and bottles and track logged drinks.
OpenZakat Calculator
Review zakatable assets, eligible debts, nisab and the standard 2.5% calculation.
OpenChoose a tool that fits your question.
Specific tasks
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Units and formats
Choose from the units and currency formats offered by each tool.
Formulas and examples
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Explanations, examples and practical context to help you use these tools. These links open articles, not interactive calculators.
- Dimensional Weight Calculator: Why Shipping Costs More Than It Weighs Read guide
- Due Date Calculator: IVF Transfer vs Conception Date Read guide
- Explore BMI Calculator: Your Guide to BMI Understanding Free 2026 Read guide
- Prayer Time Calculator Settings: A Timetable Check Worksheet Read guide
- How Are Islamic Prayer Times Calculated? Read guide
- How Is a Due Date Calculated? Naegele’s Rule Explained Read guide
- How Is a Mortgage Payment Calculated? Read guide
- How Is EMI Calculated? Formula, Worked Examples, and Amortization Read guide
- How to Calculate a Ratio (and Simplify It) Read guide
- How to Calculate a Tip: Formula, Examples & Shortcuts Read guide
- How to Calculate Age From Date of Birth Read guide
- How to Calculate Area: Formulas for Every Shape Read guide
- How to Calculate Average Speed Read guide
- How to Calculate Body Fat Percentage at Home (Navy Method) Read guide
- How to Calculate Business Days Between Dates Read guide
- How to Calculate Days Between Two Dates Read guide
- How to Calculate Discounts and Sale Prices Read guide
- How to Calculate Fuel Cost for Any Trip Read guide
- How to Calculate How Much Concrete You Need Read guide
- How to calculate per-day salary: 30, 26, or 22 days? Read guide
- How to Calculate Percentage Change in Excel and Google Sheets Read guide
- How to Calculate Percentage Increase and Decrease Read guide
- How to calculate percentage of marks: simple formula Read guide
- How to Calculate Percentages: Increase, Decrease, and Difference Read guide
- How to Calculate Perimeter (Every Shape) Read guide
- How to Calculate ROI (Return on Investment) Read guide
- How to Calculate Square Footage of a Room Read guide
- How to calculate stacked discounts (don’t add them) Read guide
- How to Calculate the Average (Mean, Median, Mode) Read guide
- How to Calculate Travel Time (Distance, Speed, Time) Read guide
- How to Calculate Water Tank Capacity Read guide
- Working Days in a Spreadsheet: NETWORKDAYS Examples Read guide
- How to Calculate Your BMR (Mifflin-St Jeor Formula Explained) Read guide
- How to Calculate Your GPA (Weighted and Unweighted) Read guide
- How to Calculate Your Net Worth Read guide
- How to Calculate Your Ovulation and Fertile Window Read guide
- How to Calculate Zakat: Cash, Nisab & a Worked Example Read guide
- How to Convert a Fraction to a Percentage Read guide
- How to Convert Hourly Wage to Annual Salary (and Back) Read guide
- How to Convert Time Zones (UTC, GMT, and Offsets) Read guide
- Is Salary Calculated for 30 Days or Working Days? Read guide
- Islamic Midnight & the Last Third of the Night (How to Calculate) Read guide
- Metric vs Imperial: How to Convert Units Read guide
- Ovulation Calculator With Irregular Periods: What It Can and Can’t Predict Read guide
- Percentage to GPA: convert marks to a 4.0 scale Read guide
- Prayer Calculation Methods Compared (MWL, ISNA, Umm al-Qura & More) Read guide
- Prayer Times at High Latitude: How to Calculate When the Sun Doesn’t Set Read guide
- Retirement Calculator With Inflation: The Number Most Plans Miss Read guide
- Self-Employed Tax Planning: Income, Expenses and Estimated Payments Read guide
- Straight-Line vs Driving Distance: What Is the Difference? Read guide
- Suhoor & Iftar Times: How Ramadan Timings Are Calculated Read guide
- What Are Macros? How to Calculate Your Macronutrients Read guide
- What Is a Calorie Deficit? How to Calculate Yours Read guide
- Zakat on gold jewelry: rules and how to calculate it Read guide
- Zakat on Stocks: How to Calculate It for Trading and Long-Term Holdings Read guide
- Zawal Time: The Forbidden Time to Pray (and How to Calculate It) Read guide
Guides, tips & how-tos.
Practical articles to help you get more from every calculator.
Age Difference Between Siblings: Calculate the Exact Gap
The age difference between siblings is the time between their birth dates. For an exact answer, compare the…
Read article →September 18, 2026Zakat on Money Saved for a House: Rulings and a Worked Worksheet
Published rulings differ on savings reserved for a needed home. Identify the ruling that applies before using a…
Read article →September 18, 2026How to Calculate Sweat Rate: A Practical Exercise Example
A sweat-rate estimate can explain fluid loss in a specific session. See a worked calculation and why the…
Read article →September 18, 2026Waist-to-Hip Ratio Changes: Why a Lower Number Can Mislead
A ratio can fall because the waist gets smaller or because the hips get larger. Keep both measurements…
Read article →September 18, 2026Cubic Feet to Gallons: Convert Container Volume Correctly
One cubic foot equals approximately 7.48052 US liquid gallons or 6.22884 imperial gallons. Multiply cubic feet by the…
Read article →September 18, 2026Fluid Ounces vs Ounces: Volume and Weight Are Different
Fluid ounces measure volume; ordinary ounces measure mass. A label reading 8 fl oz describes how much space…
Read article →Check the method, inputs and limits.
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Health, tax, finance, construction and breeding estimates may need advice from a qualified professional.
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