Percentage Calculator
Calculate percent of a number, part as percent of whole, percentage change, percentage-point difference, increase/decrease and whole-from-part.
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Calculators that explain the answer.
Find a calculator, enter your numbers and see how the result is worked out. Each tool keeps the formula, assumptions and limits close to the answer so you can judge whether the estimate fits your situation.
Popular starting points
These calculators answer common everyday questions and are a good place to begin: percentages, loans, mortgages, compound interest, BMI, calories, dates and unit conversions.
Loan Calculator
Estimate amortized loan payments, total interest and total cost with a payment schedule.
Open calculatorMortgage Calculator
Estimate mortgage payments with optional taxes, insurance and clear country/region caveats.
Open calculatorCompound Interest Calculator
Project future value from starting amount, contributions, rate, time and compounding frequency.
Open calculatorBMI Calculator
Estimate body mass index with metric and imperial units, category interpretation and clear limitations.
Open calculatorCalorie Calculator
Estimate daily calorie needs using researched BMR/TDEE methods and activity assumptions.
Open calculatorDate Calculator
Add or subtract dates and calculate differences in calendar days with clear date handling.
Open calculatorUnit Converter
Convert common units across length, mass, temperature, volume, area, speed and more.
Open calculatorExplore by topic
Start with a topic, then move between calculators, formulas and guides when you need more context. This makes it easier to check related numbers without losing the original question.
Quick math and percentage checks
Use these for discounts, percentage change, averages, fractions and basic statistics when you want the calculation shown clearly.
Loans, mortgages and amortization
Estimate payment schedules, total interest and payoff tradeoffs before comparing lending scenarios.
Health and energy estimates
Use cautious screening and planning tools for BMI, calories, BMR and TDEE with limitations kept close to the result.
Investment growth
Model compound interest, present value, future value and retirement assumptions without treating projections as guarantees.
Dates, time and units
Convert time spans, dates, currencies and units with transparent assumptions about calendars, data sources and conversion factors.
Business and SaaS metrics
Calculate CAC, LTV, MRR, ARR, ROAS and runway with definitions that make metric comparisons less ambiguous.
Construction and materials
Estimate area, concrete, paint, flooring, roofing and other project quantities with waste and measurement caveats.
Calculator categories
Start with the topic closest to your question. Financial and health estimates include extra caveats, while math, unit and date tools focus on transparent formulas and quick checks.
Financial calculators
Loan, mortgage, interest, inflation, salary and retirement calculators with clear assumptions and source-backed methodology.
103 available calculators
Open categoryHealth & fitness calculators
Health and fitness estimates that show formulas, limits and medical disclaimers instead of presenting estimates as diagnoses.
33 available calculators
Open categoryMath calculators
Everyday and advanced math tools with formulas, examples and step-by-step result explanations.
55 available calculators
Open categoryDate & time calculators
Date differences, time durations, age, schedules and calendar tools built for quick answers and clear edge-case handling.
20 available calculators
Open categoryUnit converters
Metric, imperial and scientific unit conversions with transparent conversion relationships and locale-aware formatting.
3 available calculators
Open categoryConstruction & home calculators
Practical home, area, volume, materials and renovation calculators with measurement-unit clarity.
28 available calculators
Open categoryBusiness calculators
Margin, markup, break-even, payroll and business planning calculators with careful handling of region-specific rules.
39 available calculators
Open categoryEducation calculators
GPA, grade, study planning and academic calculators with grading-system caveats.
6 available calculators
Open categoryScience calculators
Physics, chemistry and science calculators using documented formulas and units.
28 available calculators
Open categoryLifestyle calculators
Everyday planning calculators for tipping, travel, food, events and personal decisions.
16 available calculators
Open categoryStatistics calculators
Statistics tools that show methods, formulas, sample vs population choices and readable explanations.
13 available calculators
Open categoryAutomotive calculators
Fuel, mileage, trip cost and vehicle calculators with unit and currency flexibility.
11 available calculators
Open categoryTravel calculators
Travel cost, time zone, distance, currency and planning calculators with data freshness notes where needed.
10 available calculators
Open categoryTechnology calculators
Storage, bandwidth, screen, data transfer and technical calculators with standards-aware units.
26 available calculators
Open categoryHow CalcMentor explains results
A calculator is more useful when you can see what it did. CalcMentor pages show the formula or method, explain the main assumptions and limitations, and point you to related tools when another calculation may help.
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