BMI Calculator
Calculate Body Mass Index from height and weight in metric or imperial units, see your WHO category and your healthy weight range.
Free Online Calculators & Tools
One hundred fast, accurate, no-sign-up calculators for money, health, business, math and everyday life — all free, all running in your browser, and not one of them asks who you are.
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These twelve account for most of what people come here to work out. Each one runs the moment you type, shows the formula it used, and links to the tools that answer the next question.
Money questions cluster at the top — a mortgage payment, what a loan really costs, what a compounding balance becomes in twenty years. Health sits close behind, mostly BMI and daily calories. Then come the small, constant ones: a percentage, a discount, an exact age, the square footage of a room before ordering flooring. None of them need an account, and none of them send your numbers anywhere. Pick one and the answer is on screen before you finish reading this paragraph.
Mortgage Calculator
Build a full monthly housing payment — principal, interest, tax, insurance, HOA and PMI — with a complete amortisation schedule.
Percentage Calculator
Three modes in one tool: what is X% of Y, X is what percent of Y, and the percentage increase or decrease between two numbers.
Compound Interest Calculator
See what a starting balance and a monthly contribution grow into once interest starts earning interest, with a year-by-year breakdown.
Loan Payment Calculator
Work out the fixed monthly payment on any amortising loan, plus total interest, total cost and a full payment schedule.
Profit Margin Calculator
Turn revenue and cost into a margin percentage, the figure that tells you what share of every sale you actually keep.
Age Calculator
Get an exact age in years, months and days from any birth date, plus total days lived and a countdown to the next birthday.
Calorie Calculator
Get maintenance calories plus cutting and bulking targets, with the weekly weight change each target implies.
Discount Calculator
Apply single or stacked discounts, add tax, and see the final price, the amount saved and the true effective discount rate.
GPA Calculator
Convert letter grades and credit hours into a 4.0 grade point average, with a weighted option for honours and AP courses.
Square Footage Calculator
Measure rooms of any shape, add them together, and convert the total between square feet, square metres and square yards.
ROAS Calculator
Get return on ad spend as a ratio, then compare it with the break-even ROAS your gross margin actually requires.
Nine shelves
Browse by category
Every calculator lives in exactly one category, and every category page explains which tool to reach for when two of them look similar.
The split is deliberate rather than alphabetical. Finance is the largest shelf at twenty tools, because personal money questions branch further than any other topic — interest, debt, budgets, retirement and the arithmetic underneath all of them. Mortgage and real estate gets its own shelf rather than sitting inside finance, because buying property has its own vocabulary: escrow, PMI, closing costs, cap rate. Business and ecommerce are likewise separated: margin and break-even apply to any company, while fee stacks and dimensional weight are specific to selling online. Marketing and SEO holds the campaign metrics, math and statistics the general-purpose arithmetic, health and fitness the body-composition and energy formulas, construction the quantity take-offs, and education, time and everyday the grades, dates and shift hours that come up every week.
Finance & Personal Money
20 calculatorsWork out what your money does over time: interest, savings, debt payoff, retirement targets and the household budget behind all of it.
- Compound Interest
- ROI
- Retirement
- Debt Payoff
Mortgage & Real Estate
10 calculatorsPrice a home loan properly — payment, escrow, affordability, equity, closing costs and whether renting still beats buying where you live.
- Mortgage
- Mortgage Affordability
- Home Loan
- Rent vs Buy
Business
10 calculatorsMargin, markup, break-even, growth and unit economics — the numbers that decide whether a business is actually working.
- Profit Margin
- Markup
- Break-Even
- Business ROI
Ecommerce
10 calculatorsFee stacks, shipping weights, pricing back-solves and true profit per order for Shopify, Amazon FBA and any store you run.
- Ecommerce Profit
- Amazon FBA Profit
- Discount
- Shopify Profit
Marketing & SEO
10 calculatorsCampaign maths in one place: CTR, CPC, CPM, ROAS, conversion rates, email engagement and the value of the traffic you rank for.
- Conversion Rate
- ROAS
- CTR
- CPC
Math & Statistics
10 calculatorsPercentages, fractions, ratios, roots, probability, standard deviation and area — with the working shown, not just the answer.
- Percentage
- Fraction
- Average
- Ratio
Health & Fitness
10 calculatorsEstimate BMI, BMR, TDEE, macros, body fat, hydration and running pace using the published formulas clinicians and coaches use.
- BMI
- TDEE
- Calorie
- BMR
Construction & Home Improvement
10 calculatorsQuantities before you buy: concrete, gravel, mulch, paint, tile, flooring, roofing, sand, square footage and running electricity costs.
- Square Footage
- Concrete
- Gravel
- Mulch
Education, Time & Everyday
10 calculatorsGPA, grades, attendance, ages, date gaps, shift durations and paid work hours — the small calculations that come up every week.
- GPA
- Final Grade
- Age
- Grade
Real problems
What you can actually work out here
Not a feature list — the specific questions these hundred tools were built to answer.
Money you have, money you owe
The two questions underneath most personal finance are "what will this grow into?" and "what is this costing me?". The Compound Interest Calculator answers the first: put in a starting balance, a monthly contribution and a rate, and it shows the split between what you paid in and what the interest added. The Credit Card Interest Calculator answers the second, turning a balance and an APR into a payoff date and a total interest figure that is usually larger than people expect. Between them sit the planning tools — the Retirement Calculator for a retirement gap in today's money, the Emergency Fund Calculator for how many months of essential spending you actually have in reserve, and the Savings Rate Calculator, which converts a monthly surplus into an estimate of how many working years stand between you and financial independence. If you are carrying several balances, the Debt Payoff Calculator runs snowball and avalanche side by side so you can see what the difference is worth in months and in interest.
Buying, selling and renting property
A mortgage quote is one number hiding six. The Mortgage Calculator builds the whole monthly payment — principal, interest, property tax, insurance, HOA and PMI — then prints the amortisation schedule so you can see how little of an early payment touches the balance. Before that comes the Mortgage Affordability Calculator, which works backwards from income and existing debts to the price a 28/36 debt-to-income test will actually approve. Around them: the Down Payment Calculator for the cash you need up front and the point where PMI drops away, the Closing Cost Calculator for the fees that appear on the settlement statement, and the Rent vs Buy Calculator for the question that has no universal answer — whether buying beats renting over your particular horizon. Landlords get the Rental Yield Calculator and the Property Investment Calculator for cap rate, cash-on-cash return and whether a deal clears its costs.
Whether the business is working
Margin is the first honest test. The Profit Margin Calculator turns revenue and cost into the share of each sale you keep; the Markup Calculator converts between margin and markup, which are different numbers that people routinely swap by accident. The Break-Even Calculator finds the volume where fixed costs are finally covered. For online sellers the arithmetic gets denser: the Amazon FBA Profit Calculator stacks referral fees, fulfilment, storage, returns and PPC to produce a real profit per unit and a break-even ACoS, while the Shopify Profit Calculator does the same for plan fees and payment processing. When you need to set a price rather than check one, the Product Pricing Calculator back-solves the number that hits your target margin after every percentage and per-order fee has been taken out.
Whether the marketing is working
Campaign metrics are simple divisions that get compared incorrectly. The ROAS Calculator gives return on ad spend as a ratio and, more usefully, the break-even ROAS your gross margin requires — a 3.0 ROAS is excellent at 60% margin and a slow loss at 25%. The CPC Calculator and CPM Calculator price traffic; the CTR Calculator and Conversion Rate Calculator convert it. The SEO Traffic Value Calculator puts an advertising value on an organic ranking by combining search volume, a position CTR curve and cost per click, which is the closest thing to a defensible number for what SEO work is worth.
Bodies, buildings and everything else
Health starts with the BMI Calculator and moves through the BMR Calculator, TDEE Calculator, Calorie Calculator and Macro Calculator — a chain where each tool feeds the next, from resting metabolism to a daily calorie target to the protein, carbohydrate and fat grams behind it. Construction is about ordering the right quantity once: the Concrete Calculator for slabs and footings, the Paint Calculator for wall area minus doors and windows, the Flooring Calculator for boxes including waste, and the Square Footage Calculator that underpins all of them. And then the everyday shelf, which is quietly the most used of all — the Age Calculator for an exact age in years, months and days, the Final Grade Calculator for what you need on a final exam, the Work Hours Calculator for a week of shifts and overtime, and the Percentage Calculator for the three or four percentage questions that come up every single day.
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Why this site
Six promises, and what they cost you
Nothing. That is the point of listing them.
Most calculator sites are built to capture something — an email address, a lead, a click into a product funnel. This one is built to answer the question and get out of the way. The trade is straightforward: the pages carry advertising, and in exchange the tools stay open, the formulas stay published, and nothing you type is collected. If that sounds like a low bar, compare it with the last mortgage calculator that asked for your phone number before showing you a payment.
Free, permanently
No trial, no paywalled results, no premium tier holding the useful output hostage. Advertising pays for the site; the calculators do not change based on whether you see an ad.
No sign-up, ever
There is no account system to sign up to. Nothing here is gated, so there is nothing to register for and no email address to hand over first.
Works on whatever you have
Every page is built for a 360px phone first and scales up. Inputs are large enough to hit with a thumb, results stick to the bottom of the screen as you scroll, and dark mode follows your system setting.
The formula is on the page
Each calculator publishes the exact formula it runs, defines every variable, and shows at least one worked example computed by hand. If you disagree with a result you can check it.
Privacy by construction
The arithmetic happens in your browser. Your salary, your weight and your loan balance are never transmitted, because there is no server to transmit them to.
Reviewed and dated
Every page carries the month it was last reviewed. When a fee schedule or a guideline changes, the page and its worked example are updated together.
From the blog
Longer explanations
When a calculator needs more context than its own page can carry, it gets an article.
Precision Is Not Accuracy: How Much to Trust a Calculated Number
Software supplies unlimited precision at no cost, which makes it very easy to produce a figure that is exact and wrong.
Why Every Calculator Here Runs in Your Browser
There is no technical reason for a mortgage calculator to send your salary anywhere. Disconnect the internet and check.
Dates Are Harder Than They Look
From the 1st to the 8th is seven days apart and spans eight. Nearly every date argument starts there.
Questions
Frequently asked questions
Yes — all one hundred of them, with no trial period, no locked results and no premium tier. The site is paid for by advertising, which is why you will see clearly labelled ad slots on the pages. No calculator changes its output based on advertising, and none of them ask for payment details.
There is no account system at all. Nothing on factonisam is gated behind a login, so there is nothing to register for. Your starred tools and recently used list are stored by your own browser, which is why they follow you between visits on one device but not between devices.
The arithmetic is exact to the rounding shown on each page: money to two decimal places, percentages to two, scientific results to four significant figures. Accuracy of the answer, though, depends on your inputs and assumptions — a retirement projection is only as good as the return rate you assume. Every page publishes its formula so you can check the working.
No. Calculations run in your browser and the numbers never leave it. There is no server-side application and no database on this site to receive them. The only things saved are your theme choice, your favourites and your recent tools, all in your browser's local storage.
Yes. Use them to quote a job, price a product, plan a build or check a client's figures. The results are estimates for your own decision-making rather than certified advice, so for anything with legal or financial consequence have a qualified professional confirm the numbers.
They are designed for a phone first. Inputs meet the 44-pixel touch-target minimum, sliders are draggable with a thumb, the headline result sticks to the bottom of the screen as you scroll through the explanation, and every layout is tested from 360 pixels upwards.
Please do. Email info@factonisam.com with what you want to work out and, if you have one, the formula you expect it to use. Requests that come with a worked example tend to get built fastest, because half the research is already done.
Each page carries a visible review date. Tools built on fixed mathematics — percentages, area, date differences — rarely change. Tools that depend on published fee schedules or health guidelines are reviewed when those sources change, and the worked example is updated in the same pass so the page never contradicts itself.
One hundred tools, no gate
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