← Home

Calculators

71 tools

Frequent calculators, unit conversion, and production math

About This Category

This is LittleOne's Calculators & Conversions category, with 71 tools across six task clusters: everyday & shopping, units & measurement, size/screen/print, finance & planning, health & body, and education. Each tool solves one specific problem — type your numbers, see the result, all computed locally in your browser.

Everyday & Shopping

Handle common daily, date, and shopping calculations

🎂
Age Calculator
Calculate exact age and day difference from birth date with timezone aware handling.
🪙
Coin Flipper
Flip a coin online with 3D animation, multi-coin mode, decision helper, and session statistics — powered by cryptographic randomness.
Countdown Timer & Stopwatch
Unified countdown timer and stopwatch with up to 10 concurrent timer cards, natural-language input, serialized alarm queue, local restore, cross-tab sync, voice announcements, custom preset editor (drag-reorder, color-coded, shareable link), 15 ready presets (Pomodoro, Tabata, egg, ramen, meditation, meeting), multi-step engine, Web Audio bells, Wake Lock, fullscreen big display, and shareable URL. Timers run in the current browser with no login required and do not rely on a LittleOne Tools timer backend.
📅
Date Calculator
Calculate date differences, date offsets, business-day offsets, and lookup ISO week, quarter, leap year, lunar, zodiac, and solar-term details.
📆
Day of Year Calculator
Find the day number for any date, reverse-lookup a day number to its date, and view a full year calendar table with progress bar, ISO week, and quarter info.
🏷️
Discount Calculator
Calculate discount amount, sale price, and savings online.
✍️
Electronic Signature Pad
Free online electronic signature pad: handwrite with mouse / finger / stylus, with Apple Pencil pressure, palm rejection, quadratic Bézier smoothing + velocity-responsive stroke width, stroke-level undo/redo (including undoable clear), three brushes (pen / marker / highlighter), three preset colors + custom. Export transparent PNG @1x/@2x/@3x, white-background JPG, or vector SVG (auto-trimmed bounding box with optional padding), copy to clipboard. Browser-local, no uploads, no login.
📅
Leap Year Calculator
Check if a year is a leap year, list leap years in a range, with step-by-step rule verification and statistics.
🌙
Lunar / Gregorian Calendar Converter
Bidirectional conversion between Gregorian and Chinese lunar calendar (1900-2100). Four modes: single-day lookup (three-pillar Ganzhi, zodiac, lunar month names, precise solar-term times), 6×7 month grid (dual-labeled Gregorian + lunar + solar term + festival), batch conversion (multi-line paste or CSV / JSON upload, up to 1000 rows), and annual lookup of 18 lunar festivals + 24 solar terms. Handles leap-month disambiguation, .ics calendar download, and URL share links. Client-side computation, no app backend, no login.
📊
Percentage Calculator
Calculate X% of Y, find percentage share, reverse a percent, and measure percentage change.
🎯
Random Picker & Grouper
Paste a list and one click covers name picking, prize draws and team grouping. Your data is not uploaded by the tool.
Reaction Time Test
Free online reaction-speed self-test: Simple RT (tap when signal turns green), Choice RT (4-color choice response), and Go/No-Go (respond to green, not red). Configurable 3 / 5 / 10 / 20 trials, sub-millisecond timing with double-rAF baseline, false-start detection, MAD-based outlier rejection, median / SD / IQR statistics, and 6-tier neutral performance banding. Mobile-first (touch-action manipulation, full-screen tap zone, ≥72px targets), fully bilingual, keyboard-accessible, reduced-motion aware, optional 30-day local history, setup-only share URLs, PNG result poster export. Browser-local — no login, default no ad scripts, default no third-party analytics, no upload. For entertainment and personal reference only; not a medical, psychological, or neurological assessment, and not a substitute for professional driver-license testing.
💵
Tip Calculator
Calculate tip amount, per-person split, and total bill online.
💼
Workday Calculator
Local workday calculator: 5-market statutory holidays (CN/US/UK-EW/UK-SCT/UK-NIR/HK/JP, 2023-2027) + State Council 调休 / EO 11582 observed rule + custom holidays + 3 modes (count between dates / add-subtract / classify single day) + Excel NETWORKDAYS.INTL / WORKDAY.INTL compatibility + 17 weekend codes + 14-day calendar strip + fail-closed URL share. Mobile 44px touch-first. No login, default no ad scripts, default no third-party analytics.

Units & Measurement

Cover length, area, temperature, time, and related conversion

Size, Screen & Print

Handle sizing, screen, and output-oriented calculations

Finance & Planning

Handle loans, returns, and financial planning math

📊
Amortization Calculator
Free amortization calculator for generating a payment-by-payment schedule with principal, interest, remaining balance, and yearly summaries for a fixed-rate loan.
📈
APR Calculator
Free APR calculator for estimating APR, monthly payment, and net amount received on a fixed-rate installment loan using the loan amount, quoted annual rate, term, and required finance charges. Educational estimate only; not an official disclosure, lender quote, or financial advice.
🚗
Auto Loan Calculator
Free auto loan calculator for estimating financed amount, monthly payment, total payment, and total interest using vehicle price, down payment, trade-in value, payoff, rebate, taxes, fees, annual rate, and term in months.
⚖️
Break-Even Calculator
Estimate contribution margin, break-even units, and break-even sales from fixed costs, variable cost per unit, and selling price per unit. Educational estimate only; not financial, tax, legal, accounting, or pricing advice.
🧾
Federal Income Tax Calculator
Estimate 2025 U.S. federal taxable income, income tax, and effective tax rate for standard-deduction ordinary-income scenarios. Supports four manually selected filing statuses and local-only calculation. Educational estimate only; not tax, legal, or financial advice, and not a filing tool.
📊
Inflation Calculator
Estimate equivalent buying power, cumulative inflation, and average annual change between two years using historical U.S. CPI-U annual averages. Educational estimate only; not financial, investment, tax, legal, or budgeting advice.
💵
Loan Calculator
Free online loan calculator for estimating monthly payment, total payment, and total interest on a fixed-rate installment loan.
🏠
Mortgage Calculator
Mortgage calculator for principal-and-interest (P&I) estimates. Enter loan amount, annual rate, and term to estimate monthly payment, total payment, and total interest.
🏡
Refinance Calculator
Free mortgage refinance calculator for comparing your current loan with a new fixed-rate refinance scenario. Estimate payment change, total payment, interest, refinance costs, and a simple break-even period for P&I only.
📈
ROI Calculator
Estimate investment gain, total ROI, and annualized ROI from your total cost, final value, and holding period. Educational estimate only; not investment advice.
💰
Savings Calculator
Estimate ending balance, total contributions, and interest earned from an initial deposit, fixed monthly contribution, time horizon, and estimated APY. Educational estimate only; not financial, investment, tax, legal, or accounting advice.
🧮
Simple Interest Calculator
Estimate simple interest and total amount from a principal, annual rate, and time horizon. Educational estimate only; not for compound interest, APR, or amortized loans, and not financial, investment, legal, or tax advice.

Health & Body

Handle body metrics and related calculators

⚖️
BMI Calculator
Calculate adult BMI from height and weight using the standard formula and view the public reference category. For general information only; not medical advice or a diagnosis.
🔥
BMR Calculator
Estimate adult basal metabolic rate (BMR) from age, formula sex, height, and weight using the Mifflin-St Jeor formula. For general information only; not medical or nutrition advice.
💪
Body Fat Calculator
Estimate adult body-fat percentage using Deurenberg BMI-based and U.S. Navy (Hodgdon-Beckett) formulas with metric and imperial inputs. Returns ACE category, fat mass, lean mass, FFMI, and a Jackson-Pollock ideal body-fat reference. For general information only; not medical advice.
👁️
Color Vision Self-Test
Ishihara-style online self-test: 24 programmatically generated pseudoisochromatic plates automatically classify red / green / blue channel anomaly patterns and severity. Quick (10 plates) and standard (24 plates) modes; mobile-optimized; bilingual. Browser-local, no login, default no ad scripts, default no third-party analytics — results are not uploaded by the tool. For reference and self-understanding only; not a medical diagnosis. Consult an eye-care professional if you have concerns.
🗓️
Due Date Calculator
Calculate due dates from start date and offsets for business-day or calendar-day scenarios.
📆
Ovulation Calculator
Estimate your ovulation date and fertile window from the first day of your last period and your average cycle length. For general information only; not medical advice, a diagnosis, or birth control.
TDEE Calculator
Estimate adult TDEE from age, formula sex, height, weight, and activity level using the Mifflin-St Jeor formula and fixed activity multipliers. For general information only; not medical, nutrition, or training advice.

Education

Handle grades, GPA, and school-related calculations

🔢
Factorial Calculator
Compute n! (factorial), n!! (double factorial), and !n (subfactorial) with BigInt precision, digit counts, and trailing-zero analysis.
🐇
Fibonacci Calculator
Compute the nth Fibonacci number, generate the first n terms, or check whether a number is Fibonacci. BigInt precision with golden-ratio convergence analysis.
🎯
Final Grade Calculator
Calculate the final exam score you need from your current grade, final weight, and target course grade.
½
Fraction Calculator
Free online fraction calculator supporting arbitrary-operand add/sub/mul/div with integer powers. Natively parses mixed numbers, repeating decimals (0.(3)), percents, and Unicode fraction characters (½ ¼ ⅓). BigInt exact arithmetic with auto-reduce, simultaneous display of improper/mixed/repeating-decimal/percent/LaTeX forms, and step-by-step LCM/combine/GCD explanation plus pie-chart and number-line visuals.
📐
Geometry Calculator
All-in-one geometry calculator for 25 common 2D shapes and 3D solids — area, perimeter, volume, surface area. Reverse-solve from any known value, with parameter-responsive SVG diagrams, substituted formula steps, per-field unit conversion, and adjustable significant figures / π precision.
🧮
Prime Factorization Calculator
Factor integers into primes, list all divisors with factor pairs, and test primality — with step-by-step process and large number support.
🔗
GCD & LCM Calculator
Calculate GCD and LCM for multiple integers with Extended Euclidean Algorithm and Bézout's identity. Shows step-by-step Euclidean and prime factorization methods.
🎓
GPA Calculator
Calculate GPA from course credits and letter grades with weighted grade points and total credits.
📝
Grade Calculator
Calculate weighted course grades from assignments, quizzes, midterms, and finals.
🧮
Matrix Calculator
Local matrix calculator with multi-matrix expressions, exact fraction arithmetic, step-by-step teaching, LU/QR/Cholesky decompositions, 2×2/3×3 eigenvalues, and Excel/CSV/MATLAB/NumPy/LaTeX paste. No login, default no ad scripts, no upload.
🌀
Maze Generator
Local maze generator: 3 algorithms (Recursive Backtracker / Prim / Kruskal), reproducible seeds, A4 printable with optional answer page, QR code for mobile sharing, daily challenge seed. Includes dead-end highlight, shortest-path solver, PNG/SVG export. No login, default no ad scripts, no upload.
📊
Variance & Standard Deviation Calculator
Education-grade + research-grade descriptive statistics calculator: 13 core statistics (mean, median, mode, variance, SD, range, quantiles, IQR, ...) + 3 education modes (China high school / international / research) + denominator toggle (n-1 / n) + 3 SVG charts (histogram / box plot / QQ-plot) + normality tests (Jarque-Bera + D'Agostino K²) + 3-method outlier detection + multi-delimiter paste + 4-format export. Welford+Kahan compensated numerical core.
🧩
Sudoku Generator
Local Sudoku generator and game with real 5-level technique-based difficulty (Easy/Medium/Hard/Expert/Evil), triple highlighting (row-col-box/same-number/selected), auto-pencil candidates, 4-stage progressive hints, local best times, daily puzzle, URL sharing, 200-step undo/redo, dark mode. Mobile-friendly 44px touch targets. No login, default no ad scripts, no upload, default no third-party analytics.
🎴
24 Game Solver
Enter 4 playing cards (A/J/Q/K letters or 1–13 numbers) and see every expression that makes 24. Features exact rational arithmetic (catches fraction solutions like 8÷(3−8÷3)), equivalence dedup, bracket-minimized display, custom target, random deal, and classic hard-case presets. Works on desktop and mobile.

Related Hubs

Use Limits

This category includes finance and health sensitive tools. Results come from fixed formulas — these tools do not connect to any financial institution, tax system, or medical service. For real loan, home-buying, tax, investment, or health decisions, consult a licensed professional. See the finance-specific and health-specific sections of the disclaimer.