Calculators & Converters
Free online calculators and unit converters for finance, health, math, science, home improvement and everyday questions. Every calculator runs entirely in your browser — instant results, no signup, nothing sent to a server.
From a quick percentage to a full mortgage amortisation schedule, this is the largest collection of free online calculators and unit converters on Gera Tools — covering finance, health and fitness, maths, physics, chemistry, cooking, construction and dozens of everyday questions. Each one is a single-purpose calculator that gives you an exact answer instantly, shows the formula it used, and never asks you to sign up.
Every calculator runs entirely in your browser. Your numbers are never uploaded to a server, stored, or logged — which makes these tools safe for sensitive figures like salary, loan balances or medical values. Search by name above to jump straight to the calculator you need, or browse the grouped sections below.
Start here — our most useful calculators & converters
Hand-picked from the full collection of 2286 tools.
Percentage Calculator
Handles every form of percentage question — X% of Y, percent change, difference and reverse percentages — and shows the working.
Compound Interest & Savings Calculator
Projects savings growth with regular deposits and compounding, so you can see what a habit is worth over years.
Loan & Personal Credit Calculator
Monthly payment, total cost of credit and representative APR for any loan amount and term.
BMI / BMR / TDEE Calculator
BMI, basal metabolic rate and daily calorie needs together in one tool instead of three.
Unit Converter
Length, weight, temperature, volume, area and speed in a single instant converter.
Age Calculator
Your exact age in years, months and days, plus a countdown to the next birthday.
Browse calculators & converters by topic
- Aldosterone-to-Renin Ratio (ARR) Calculator
- Bone Marrow Blast Percentage Calculator
- Bow Arrow Kinetic Energy & FOC Calculator
- VAT & Sales Tax Calculator
- Take-Home Pay & Salary Tax Calculator
- Saudi Arabia & UAE VAT Calculator (GCC) — Arabic RTL Friendly
- Blood Alcohol Calculator (BAC)
- Aminoglycoside Extended-Interval Dosing Nomogram
- APGAR Score Calculator
- Economizer Changeover Temperature & Enthalpy Calculator
- Aquarium CO2 / pH / KH Calculator
- Dilution Calculator (C₁V₁ = C₂V₂)
- Concrete Pump Friction Loss Calculator
- Crossbow Kinetic Energy Calculator
- HVAC Duct Friction Loss Calculator
- Three-Phase Voltage Imbalance Calculator
- Audio Transformer Turns Ratio & Impedance
- Bar Exam MBE & Scaled Score Calculator
- Australia Pension & Retirement Calculator
- Automotive Gear Ratio & Speed Calculator
- Boiler Horsepower & Steam Output Calculator
- Audio Buffer Size & Latency Calculator
- Mix Bus Clip Headroom Calculator
- Theoretical Noise Floor by Bit Depth Calculator
- Bicarbonate Deficit Calculator
- Solidity Gas Limit Estimator
- Bitcoin Difficulty & Block Time Estimator
- Agricultural Water Quality Compliance Checker
- Cookie Consent Compliance Checker
- Data Transfer Mechanism Selector (GDPR / UK GDPR)
- Lunar Phase & Moonlight Exposure Calculator
- Moon Phase & Illumination Calculator
- Astrophoto Golden Hour & Astronomical Twilight Calculator
- Bolt Circle Coordinate Calculator
- Compass Deviation & Variation Correction Tool
- Great-Circle Aviation Route Calculator
- Catan Dice Roll Probability Analyzer
- Darts Scoring Probability Calculator
- Motor KV & Propeller Combination Calculator
- CO2 Cylinder Duration Calculator
- Bokeh Circle of Confusion Size Calculator
- Climbing Grade Pyramid Builder
- ACT Score Percentile Calculator
- Date Add/Subtract Duration
- Phenytoin Free Fraction Estimator in Renal Failure
- Beeswax Food Wrap Recipe Calculator
- Lab Buffer Recipe Generator
- Cooking Measurement Conversion Reference
- Aquaculture Stocking Density Calculator
- Aquarium Alkalinity (KH) & Buffer Calculator
- Aquarium CO2 Bubble Count Rate Calculator
- Age Calculator
- Age-Appropriate Design Code Checker
- Beers Criteria High-Risk Drug Checker for Older Adults
- Astrophotography Target Framing Calculator
- Astrophotography Mosaic Panel Calculator
- Astrophotography Total Exposure Calculator
- Alveolar-Arterial (A-a) Gradient Calculator
- Paracetamol Toxicity Nomogram (Rumack-Matthew)
- Anaesthetic Gas Flow Rate Calculator
- Sill Plate Anchor Bolt Layout Calculator
- Boring Bar Deflection Calculator
- Center Drill Depth Calculator
- Box Fill Calculator (NEC 314.16)
- Bundling (Adjustment Factor) Derating Calculator (NEC 310.15(C))
- Busbar Ampacity Calculator
- AI Training Data Rights Checker
- Air Cargo Revenue Tonne-Kilometre Calculator
- Ballast Calculation Tool
- AI Model Training Carbon Estimator
- Carbon Inset vs Offset Decision Tool
- CBAM Certificate Quantity & Cost Planner
- ADA / Section 508 Accessibility Checklist
- EU AI Act Conformity Assessment Pathway
- AI Liability Risk Scorer (EU AI Liability Directive)
Frequently asked questions
Are these calculators really free?
Yes. Every calculator on Gera Tools is free to use with no account, no trial and no usage limit. The site is supported by unobtrusive ads, not subscriptions.
Do my numbers get sent to a server?
No. Each calculator runs 100% client-side in your browser using JavaScript. The values you type are never transmitted, stored or logged, so they are safe for private financial, health or business figures.
How accurate are the results?
Each calculator uses the exact published formula for its field — amortisation maths for loans, the Mifflin-St Jeor equation for calories, real tax bands for take-home pay, and so on — and most show the working so you can verify it.
Can I use them on my phone?
Yes. Every tool is mobile-friendly and keeps working offline once the page has loaded, because the calculation happens on your device rather than on a server.