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2000+ free calculators, instantly.

Finance, health, math, science, unit conversion, business, food, sports, education, and daily planning. Every calculator includes the tool, formula notes, examples, FAQs, and related guides.

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Browse by topic area

Five calculator collections

Every calculator is organised into one of five topic areas. Click a collection to browse all the tools, sub-categories, and guides it contains.

Finance

137 calculators

Loans, mortgages, savings, investments, tax, budgets, retirement planning and more.

Finance
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Health & Fitness

385 calculators

BMI, calories, nutrition, body composition, fitness training, sports and wellbeing.

HealthSportsFood
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Science & Engineering

755 calculators

Physics, chemistry, construction, unit conversion, technology and technical design.

ConstructionConversionPhysicsChemistryEngineeringTechnology
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Business & Data

252 calculators

Profit margins, ROI, pricing, statistics, payroll, revenue and business planning.

StatisticsBusiness
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Everyday Life

491 calculators

Math, dates, discounts, tips, education, ecology and everyday household decisions.

MathEveryday LifeEcologyEducation
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Browse by category

Calculator categories

Each category page works like a focused mini-library with topic clusters, descriptions, internal links, and calculator pages targeting specific search intent.

Finance

Plan loans, savings, investments, taxes, budgets, interest, and everyday money decisions with clear formulas and examples.

137 calculators

Health

Estimate health, fitness, nutrition, body measurements, and wellness metrics using practical reference formulas.

135 calculators

Math

Solve percentages, ratios, fractions, averages, geometry, algebra helpers, and common school or workplace math problems.

131 calculators

Construction

Estimate materials, areas, volumes, costs, paint, concrete, flooring, roofing, and renovation quantities.

130 calculators

Conversion

Convert units for length, weight, temperature, speed, volume, area, pressure, energy, and daily measurements.

125 calculators

Physics

Work with speed, force, energy, motion, electricity, waves, pressure, and classroom science formulas.

125 calculators

Chemistry

Use chemistry helpers for concentration, molarity, dilution, gas laws, molecular mass, and lab calculations.

125 calculators

Statistics

Analyze averages, probability, samples, confidence, variation, scores, and data interpretation problems.

125 calculators

Business

Estimate profit, margins, markup, inventory, payroll, pricing, revenue, productivity, and business planning metrics.

127 calculators

Everyday Life

Quick calculators for dates, time, tips, discounts, travel, fuel, recipes, shopping, and household planning.

110 calculators

Sports

Calculate pace, performance, training zones, scores, ratios, sports statistics, and fitness planning numbers.

125 calculators

Food

Scale recipes, estimate calories, cooking conversions, ingredient weights, nutrition, and meal planning quantities.

125 calculators

Ecology

Estimate energy use, water use, carbon footprint, recycling, transport impact, and sustainable living metrics.

125 calculators

Engineering

Work through mechanical, electrical, civil, and systems engineering formulas for practical design checks.

125 calculators

Education

Support learning with grade, score, GPA, reading, study time, classroom math, and academic planning calculators.

125 calculators

Technology

Estimate bandwidth, storage, download time, screen sizes, data transfer, battery life, and computing metrics.

125 calculators

Accuracy and transparency

Why United Calculator

Every page follows the same content standard: formula derivation, a worked example with real numbers, applicable laws or professional guidance, 6 plain-language FAQs, and links to 8 related tools.

Verified formulas

Each formula engine is based on published standards — TILA for loan calculations, METS tables for energy expenditure, ASTM standards for materials, and equivalents across 16 subject areas. The formula is shown in a code block on every result card so you can verify the calculation independently.

Professional context, not professional advice

Finance and health calculators cover applicable legislation (CFPB, NHS, OSHA) and reference professional thresholds (e.g. debt-to-income ratios accepted by lenders, WHO BMI categories). Every page includes a disclaimer — these tools are planning aids. Consequential decisions should be reviewed with a qualified professional.

No account, no tracking, no fee

Calculations run entirely in your browser. No data leaves your device. There are no login walls, no usage limits, no subscription tiers, and no premium paywalls. The only data stored is nothing — no cookies are set beyond what your browser requires to render the page.

Transparent methodology

Smart defaults come from published benchmarks — median UK household income from ONS, US average mortgage rate from Freddie Mac weekly surveys, average commute distances from the US Census ACS. Defaults are documented in the article body on each calculator page.

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Simple by design

How United Calculator works

Three steps from question to answer — no account, no subscription, no ads cluttering the result.

Search or browse

Type a topic into the search box or click a category. Each category is a mini-library of 125 calculator pages targeting specific questions — loan payments, BMI, tile counts, carbon footprint, and more.

Enter your values

Smart defaults are pre-filled so you get an immediate example result. Replace any field with your own data. Click the ? icon on any field for a plain-language explanation of what that input means.

Read, copy, and share

The result updates in real time. The formula is shown in a code block below the answer. Copy the result to your clipboard, share it to 8 social platforms, or scroll down for the full explanation, FAQs, and 8 related calculators.

Price to Sales Calculator

Price to Sales Calculator: calculate price to sales for your business. Formula, benchmarks, and practical tips included.

A compound investment calculator projects the growth of an investment where returns generate additional returns — the fundamental mechanism behind 401(k) growth, dividend reinvestment, and long-term wealth accumulation. Albert Einstein reportedly called compound interest "the eighth wonder of the world," and the math justifies the claim: $10,000 growing at 10% annually for 40 years reaches $452,593 — 45× the original amount, with 98% of the final value coming from compounding rather than the original principal. and are essential companion tools for investment and retirement planning.

The S&P 500 has compounded at approximately 10.5% annually since 1928, with dividends reinvested — the most widely cited long-run US equity return benchmark. A 401(k) or IRA growing at that rate over a 40-year career turns $500/month in contributions into approximately $3.2 million. The compounding frequency (daily vs monthly vs annual) matters only marginally compared to the dominant variables: rate of return and time horizon. Getting the right account type — tax-deferred, tax-free, or taxable — has a larger impact on after-tax compounding than any frequency effect.

  1. Enter the principal (initial investment amount).
  2. Enter the annual interest or return rate as a percentage.
  3. Enter the compounding frequency: annually, quarterly, monthly, or daily.
  4. Enter the time period in years.
  5. Read the final value, total interest earned, and growth breakdown showing the power of compounding vs principal.
  6. Use the regular contributions field to model monthly deposits — the combined effect of compounding plus systematic contributions produces the most dramatic long-run results.

Compound interest formula

A = P × (1 + r/n)^(n×t) where P = principal, r = annual rate (decimal), n = compounding periods per year, t = years.

With regular contributions: FV = P × (1 + r/n)^(nt) + PMT × [(1 + r/n)^(nt) − 1] ÷ (r/n) where PMT = payment per period.

Worked example: $5,000 in a Roth IRA at 8% compounded monthly for 30 years. A = $5,000 × (1 + 0.08/12)^(360) = $5,000 × 10.935 = $54,676. Add $500/month: total = $54,676 + $745,180 = $799,856. Total contributed: $5,000 + ($500 × 360) = $185,000. Growth from compounding: $614,856 — more than 3× the total contributed.

Understanding your compound return

US compound return benchmarks (2024)

S&P 500 total return (dividends reinvested, 1928–2024): ~10.5% nominal, ~7.5% real. US Total Market index: similar to S&P 500. 60/40 stock-bond portfolio: ~7–8% nominal historically. US 10-year Treasury yield (2024): ~4.2–4.5%. High-yield savings accounts (2024): 4.5–5.2% APY. Series I Savings Bonds (Nov 2024): 3.11% composite rate. CDs (1-year, 2024): 4.8–5.5% at top online banks. Money market funds: ~5.0% (2024 federal funds rate environment). For long-term (20+ year) equity investments, 7–10% nominal is the historical base-case range.

Business tips and best practices

Common mistakes to avoid

Compound interest projections are mathematical illustrations only and do not constitute investment advice, a deposit guarantee, or a securities recommendation. Savings account, CD, and money market rates change daily and are not guaranteed beyond any stated term. FDIC insurance covers up to $250,000 per depositor per institution. Investment returns are not guaranteed and can be negative. In the US, investment advisors are registered with the SEC or regulated by FINRA. IRS rules governing 401(k) and IRA contribution limits and early withdrawal penalties change annually — refer to IRS.gov for current rules. Before making investment decisions, consult a fiduciary financial advisor.