Calculators that show the maths
Get the number. See the math behind it.
Independent, free calculators for freelancers, SaaS teams, AI builders and country tax. Every answer comes with the formula filled in with your own numbers, so you can check it before you rely on it.
No sign-up. Nothing you type leaves your browser.
Net profit needed
$80,000 ÷ (1 − 92.35% × 15.3%)equals$93,164
Self-employment tax
$93,164 × 92.35% × 15.3%equals$13,164
Revenue you need
$93,164 + $6,000 expensesequals$99,164
Billable hours a year
25 h × 47 wkequals1,175 h
Hourly rate
$99,164 ÷ 1,175 hequals$84/h
Based on an $80,000 income goal after self-employment tax (before income tax). Try it with your own numbers
How we work
Formulas, not black boxes
Every result comes with the equation and the substitution shown, so you can retrace the maths yourself.
Checked against official sources
Tax rates and prices come from the publishing authority, with a dated review on the page. How we check the math.
Updated when the world changes
When a tax rule or AI price moves, the tool and a short news post follow. Nothing goes stale quietly.
Who runs this site
Start here
See all toolsThree tools people use most. Each shows its formula and worked example on the page.
- Featured
Freelance Hourly Rate Calculator
Work out an hourly rate that actually covers your income goal, expenses, and self-employment tax, not just a guess.
Open the calculator
- Featured
SaaS Magic Number Calculator
Find out how much new annual revenue each dollar of sales and marketing spend produced, and whether it is time to spend more.
Open the calculator
- Featured
AI API Cost Calculator
Estimate the cost of OpenAI, Claude and Gemini API calls per request and per month, from tokens, words, code lines or characters, with prompt caching and batch discounts.
Open the calculator
Why MathBehind exists
Most online calculators hide the working. You type in your numbers, get a result, and have no way to tell whether the answer is right short of running the maths yourself on paper. For anything that matters — a rate you’ll quote a client, a retirement contribution, a cross-border payment — that’s not good enough.
Every tool on MathBehind shows the formula filled in with your own numbers, step by step. Every tax rate and official figure is checked against the source (IRS, HMRC, FBR, UAE FTA, Apple, OpenAI, Anthropic, and so on) before it goes live, with the review date on the page. If a rate changes, the news feed records what changed, when, and how the tool was updated.
The site is independent, free, and funded entirely by display ads. There’s no sign-up, no email capture to see your answer, and no walls of unrelated content between you and the calculator. Spot a figure that’s wrong? Email Muhammad Ahmad — we fix those within 24 hours.
What’s new
All newsPricing and tax changes we’ve updated the tools for.
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UAE Corporate Tax Year 2 (2027): What Changes, What Stays
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Inside IR35 Day Rate: What You Actually Take Home in 2026-27
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UK Contractor Outlook 2027-28: IR35, Thresholds and Autumn Budget Impact
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Start with a toolkit
All toolkitsBrowse every tool
109 calculators and converters, grouped by the problem they solve.
Rates, quotes, platform fees, invoices and getting paid.
- Freelance Hourly Rate CalculatorWork out an hourly rate that actually covers your income goal, expenses, and self-employment tax, not just a guess.
- Salary to Hourly CalculatorConvert an annual salary to an hourly rate, or an hourly rate to its annual equivalent, with your real work schedule, not a generic 2,080-hour assumption.
- Project Quote EstimatorTurn estimated hours and your hourly rate into a fixed project price, with a buffer for overruns and a deposit to ask for up front.
- Late Payment Interest CalculatorWork out the interest owed on an overdue invoice from the amount, an annual interest rate and the number of days it is late.
- Freelance Platform Fee Calculator (Upwork, Fiverr, Freelancer.com)See what you actually take home from Upwork, Fiverr or Freelancer.com after the service fee, Connects and withdrawal costs, and what to charge to keep the amount you want.
- International Payment Cost CalculatorCompare two ways of getting paid from abroad, such as a wallet, a transfer service or a bank wire. See the fees, the exchange-rate markup and how much actually arrives.
- Freelancer Tax Set-Aside CalculatorWork out how much of each client payment to put aside for income tax and social contributions, in any country, so the tax bill is never a surprise.
- Day Rate Calculator: Day Rate to Hourly and AnnualConvert a contractor day rate to an hourly rate and annual income, or work back from an hourly rate or annual target to a day rate.
- Time to Decimal Hours ConverterTurn tracked time like 4h 17m into decimal hours (4.28) for your invoice, with optional billing rounding and the amount to bill.
- Retainer Fee CalculatorPrice a monthly retainer from the hours you reserve, your hourly rate and a premium for guaranteed availability, and see what it is worth over the contract.
- Compound Interest and Savings Goal CalculatorSee what your savings grow to with compound interest and monthly deposits, and how much you'd need to save each month to hit a goal.
- Invoice Due Date Calculator (Net 30, Net 60)Find the exact due date for Net 7, Net 30, Net 60, EOM and 2/10 Net 30 payment terms, with the weekday and any early-payment discount.
- Fire Your Client CalculatorFind out what a low-paying, high-effort client really pays per hour, and whether replacing them would pay off once realistic refill time is counted.
- Retainer Inflation AdjusterSee how much a fixed retainer or rate has lost to inflation, what it should be today, and get a ready-to-send note for your client.
- Value-Based Pricing CalculatorPrice a project by the result it creates for the client, not the hours it takes, and check it against your hourly floor and the client's return.
- Scope Creep and Change Request CalculatorPrice a client's extra request against the original scope, and see what absorbing it for free would do to your real hourly rate.
- Invoice GeneratorBuild a clean, itemized invoice with your own logo, then print or save it as a PDF. No account, no watermark.
- Weekly Timesheet CalculatorAdd up a week of start and end times with breaks, in hours and minutes and decimal hours, with overtime pay and CSV export.
Income tax, sales tax and end-of-service rules for specific countries, with official sources.
- Zakat CalculatorCalculate zakat on cash, gold, silver, investments and business assets in any currency, using today's gold or silver price for the nisab.
- Saudi End of Service Benefit (Article 84/85/87) CalculatorThe half-month then full-month formula from Articles 84 and 87 of the Saudi Labor Law, with the resignation tiers from Article 85 (1/3 under 5 years, 2/3 under 10, full after).
- Pakistan Salary Income Tax Calculator 2026-27Work out income tax on your salary in Pakistan with the FBR slabs for tax year 2027 (2026-27) or 2026, including monthly deduction, take-home pay and your effective rate.
- LLC vs Sole Proprietor Tax Calculator (S Corp Election)Compare self-employment tax as a sole proprietor or single-member LLC with payroll tax under an S corporation election, after the extra costs of running payroll.
- Quarterly Estimated Tax Calculator 2026 (US Self-Employed)Estimate 2026 federal income tax and self-employment tax on 1099 freelance income, and how much to pay the IRS each quarter.
- UK Self-Employed Tax Calculator 2026/27Work out Income Tax and Class 4 National Insurance on sole trader profits for 2026/27, what to set aside, and your payments on account.
- Australia Income Tax Calculator 2026-27Calculate Australian income tax for 2026-27 or 2025-26, with the Medicare levy and Low Income Tax Offset, for employees, contractors and sole traders.
- Canada GST/HST Calculator by ProvinceAdd or remove GST, HST, PST or QST for any Canadian province or territory, with the current rates including Nova Scotia's 14% HST.
- India Income Tax Calculator FY 2026-27 (Old vs New Regime)Compare tax under the new and old regimes for FY 2026-27, for salaried people and freelancers using the presumptive scheme, with rebate, cess and monthly take-home.
- UAE Gratuity Calculator 2026 (End of Service)Calculate your UAE end-of-service gratuity under the current Labour Law: 21 days of basic pay per year for five years, then 30 days a year.
- UAE Corporate Tax Calculator for Freelancers and SMEsCheck whether UAE corporate tax applies to your freelance or small business income, and work out the 9% tax on profit above AED 375,000.
- Philippines Freelancer Tax Calculator: 8% vs GraduatedCompare the 8% income tax option with graduated rates plus 3% percentage tax for Filipino freelancers and professionals, and see which costs less.
- Nigeria Income Tax Calculator 2026 (New Tax Act)Calculate Nigerian personal income tax under the Nigeria Tax Act 2025 bands in force from January 2026, with rent relief, for salary or freelance income.
- New Zealand Income Tax Calculator 2026/27Work out New Zealand income tax and the ACC earners' levy for 2026/27, for salary, contracting or sole trader income, with take-home pay.
- SEP IRA Contribution Calculator 2026Find the most a self-employed person can put into a SEP IRA for 2026 from Schedule C profit, the tax it could save, and how a Solo 401(k) compares.
- Solo 401(k) Contribution Calculator 2026Work out the most a self-employed person with no employees can put into a Solo 401(k) for 2026: employee deferral, employer share and catch-up.
- Home Office Deduction Calculator (Simplified vs Regular)Compare the IRS simplified home office deduction ($5 per square foot) with the regular method using your actual home costs, and see which is larger.
- Mileage Deduction Calculator 2026Work out your 2026 business mileage deduction at the IRS standard rates (72.5¢ to June, 76¢ from July), plus parking and tolls, and the tax it saves.
- 1099 vs W-2 Take-Home Pay Calculator 2026Compare take-home pay from a W-2 salary with a 1099 contract after federal income tax, FICA or self-employment tax, expenses and lost benefits.
- Pakistan Freelancer IT Export Tax Calculator 2026-27Work out the section 154A tax your bank deducts on foreign freelance income (0.25% with PSEB registration, 1% without) and whether it's your final tax.
- Pakistan Property Transfer Tax Calculator 2026-27 (236K and 236C)Work out the advance tax on buying (236K) and selling (236C) property in Pakistan for 2026-27, and how much more a non-filer pays.
- Payoneer vs Wise vs Bank Transfer: PKR Received CalculatorCompare how many rupees reach your Pakistani bank account from a USD payment through Payoneer, Wise or a direct bank wire, after fees and exchange-rate markups.
- Limited Company Salary vs Dividend Calculator 2026/27Find the take-home from a UK limited company after corporation tax, National Insurance, income tax and the 2026/27 dividend rates, and compare common salary levels.
- IR35 Calculator 2026/27: Inside vs Outside Take-HomeCompare a UK contractor's take-home from the same day rate outside IR35 (limited company, salary and dividends) and inside IR35 (paid through an umbrella).
- Qatar End of Service Gratuity (21 Days/Year, Article 54) CalculatorA flat 21 days of last basic wage per year of service under Qatar Labour Law Article 54. No tier change at five years; the minimum one-year service threshold applies.
- Kuwait End of Service Indemnity (15/30 Days, 18-Month Cap) CalculatorKuwait private-sector indemnity under the Labour Law: 15 days per year for the first five years, a month per year thereafter, capped at 18 months, with the resignation step-up tiers.
- Saudi GOSI Contribution Calculator 2026Work out monthly GOSI contributions for employee and employer in Saudi Arabia, for Saudis on the old or new system and for expatriates.
- Filer vs Non-Filer Cost Calculator Pakistan 2026-27See how much more tax is deducted from a non-filer than a filer in 2026-27 on bank profit, dividends, property, cars, cash withdrawals and card spending abroad.
Churn, MRR, CAC, LTV, runway and pricing for subscription businesses.
- SaaS Unit Economics CalculatorChurn, customer lifetime value, CAC payback, and gross margin: four numbers that explain each other, calculated from one set of inputs.
- SaaS Pricing Comparison CalculatorCompare what two SaaS tools actually cost your team, at your team size and billing cycle, not their marketing-page headline price.
- MRR to ARR CalculatorConvert monthly recurring revenue to annual run rate, and see how new, expansion, and churned revenue move the number next month.
- Burn Rate and Runway CalculatorSee how much cash your company loses each month and how many months you have left before the bank balance runs out.
- Net Revenue Retention (NRR) CalculatorMeasure how much revenue your existing customers generate compared with a period ago, including upgrades, downgrades and cancellations.
- Rule of 40 CalculatorAdd your revenue growth rate and profit margin to see whether your SaaS business meets the Rule of 40 benchmark.
- Customer Acquisition Cost (CAC) CalculatorWork out what each new customer costs you from your sales and marketing spend, and how long it takes to earn that cost back.
- SaaS Churn Rate CalculatorCalculate customer churn and revenue churn for a month, annualize it correctly, and see how long the average customer stays.
- SaaS Quick Ratio CalculatorMeasure how efficiently your SaaS grows: new and expansion revenue gained for every dollar lost to churn and downgrades.
- SaaS Magic Number CalculatorFind out how much new annual revenue each dollar of sales and marketing spend produced, and whether it is time to spend more.
- Payment Processor Fee Comparison: Stripe, PayPal, PaddleCompare what Stripe, PayPal, Paddle, Lemon Squeezy and Gumroad would charge on your price and sales volume, including international buyers and tax handling.
- App Store Fee Calculator: In-App vs Web CheckoutCompare what you keep from in-app purchases after Apple's or Google's commission with what you would keep selling through your own web checkout.
- Annual vs Monthly Pricing CalculatorSet your annual plan discount with confidence: see the annual price, what customers save, and the discount at which annual earns you as much as monthly plans that churn.
- LTV to CAC Ratio CalculatorCompare what a customer is worth over their lifetime with what it costs to win them, and see how long it takes to earn the acquisition cost back.
- SaaS Valuation Calculator: ARR Multiple MethodEstimate a SaaS company's value from ARR and a revenue multiple range, see the value of your stake, and check the growth and retention signals that move the multiple.
- Price Increase Impact CalculatorSee what a price rise does to monthly revenue after the customers it costs you, and how many you could lose before it stops paying off.
- Trial to Paid Conversion CalculatorTurn trial sign-ups and a conversion rate into new customers and MRR, the acquisition cost per paying customer, and the trials you need to hit a revenue goal.
- SaaS Cohort Retention Table GeneratorPaste monthly signups and active customers to see a cohort retention heatmap, weighted averages by month, and export it as CSV.
Token pricing, chat features, context windows and GPU memory for AI products.
- API Rate Limit ConverterConvert between requests per second, minute, and day, and get a safe sustained rate with headroom built in, not just the raw math.
- AI API Cost CalculatorEstimate the cost of OpenAI, Claude and Gemini API calls per request and per month, from tokens, words, code lines or characters, with prompt caching and batch discounts.
- Token to Word Count ConverterEstimate how many tokens a piece of text will use, or how many words a token budget allows, using the standard ~4 characters per token rule of thumb.
- AI Feature Cost CalculatorEstimate the monthly API bill for a chatbot or AI feature from your users and conversations, including the cost of re-sending chat history.
- LLM Context Window CalculatorSee how a system prompt, chat history and documents fill an LLM's context window, how many turns fit before it overflows, and what each request costs.
- AI Image Generation Cost CalculatorWork out what AI-generated images really cost per usable result, once retries, variations and storage are counted, and project the monthly bill.
- Vector Database Storage CalculatorEstimate the storage and memory your embeddings need from the vector count, dimensions, precision and index type, including metadata and replicas.
- AI Fine-Tuning Cost CalculatorEstimate the cost of fine-tuning an LLM from your dataset size and epochs, then add the monthly cost of running the tuned model.
- LLM VRAM Calculator: GPU Memory to Run a ModelEstimate how much GPU memory an open-weight LLM needs for inference: model weights at your chosen precision, the KV cache for your context length, and overhead.
- Self-Host vs API LLM Cost CalculatorCompare renting GPUs to run an open model with paying per token for an API model, and find the monthly volume where self-hosting starts to pay.
- RAG Pipeline Cost CalculatorPut embeddings, vector storage and answer generation into one monthly number for a retrieval-augmented generation (RAG) app, with cost per query.
- AI Agent Cost CalculatorEstimate what an AI agent costs per task and per month when every step re-sends a growing context of tool results, with retries included.
Margins, VAT, loans, interest, ROI and everyday percentages.
- Team Cost CalculatorProject what a per-seat SaaS tool will cost as your team grows: today's bill and next year's, side by side.
- Percentage ConverterConvert between a percentage, a decimal, and a fraction, and see what X% of a number actually is.
- Subscription Cost TrackerAdd up what your subscriptions actually cost per year, once monthly and annual billing cycles are combined onto one number.
- Software ROI CalculatorTurn time saved by a tool into a dollar value, and see whether its cost actually pays for itself, and how fast.
- Percentage Change CalculatorFind the percentage increase or decrease between two numbers, and the change it would take to get back to where you started.
- Profit Margin vs Markup CalculatorEnter a cost and a selling price to see profit, margin and markup side by side, plus the price you need to hit a target margin.
- VAT and Sales Tax CalculatorAdd tax to a net price, or take it out of a price that already includes it. Works with any currency and any rate.
- Break-Even CalculatorFind how many units you need to sell each month to cover your fixed costs, and how many it takes to reach a profit target.
- Burn Multiple CalculatorDivide net new ARR by net cash burned to see how efficiently your SaaS is turning cash into growth, with the benchmarks every stage should hit.
- Contractor vs Employee Cost CalculatorCompare the full yearly cost of hiring an employee with paying a contractor for the same hours, and find the break-even contractor rate.
- Loan EMI CalculatorWork out the monthly instalment (EMI) on a loan, the total interest you'll pay, and how much of the first payment goes to interest.
- Discount Calculator: Price After DiscountFind the sale price after a percentage discount, stack a second discount on top, add sales tax, and see what you really save.
- Influencer Engagement Rate and Rate Card CalculatorCalculate engagement rate by followers and by reach, then turn your average views into a sponsorship price range for a single post and a package.
- CAGR Calculator: Compound Annual Growth RateWork out the compound annual growth rate between a starting and ending value, compare it with simple average growth, and project it forward.
- ROI Calculator: Return on Investment and Annualized ROICalculate return on investment from what you put in and what you got back, plus annualized ROI so investments held for different lengths of time compare fairly.
- Sales Commission Calculator With Quota and AcceleratorsWork out commission on sales with a base rate up to quota and a higher accelerator rate above it, plus total pay and the effective commission rate.
- Salary Raise Calculator: New Pay and Real IncreaseSee your new salary after a percentage raise, how much more you get each month, and whether the raise beats inflation.
- Business Days Calculator: Working Days Between DatesCount working days, calendar days and weeks between two dates, excluding weekends and holidays, including Sunday-to-Thursday work weeks.
- Loan Amortization Schedule CalculatorA month-by-month and yearly amortization table for any loan, with extra payments, interest saved and CSV download.
Timestamps, units, colours, subnets, permissions and uptime.
- Unix Timestamp ConverterConvert a Unix timestamp to a human-readable UTC date, or the reverse. Instant, with no rounding surprises.
- Number Base ConverterConvert a number between binary, octal, decimal, and hexadecimal, instantly, in either direction.
- Color Code ConverterConvert a HEX color to its RGB and HSL equivalents, instantly, with the exact values CSS expects.
- Data Storage ConverterConvert between bytes, KB, MB, GB, TB, and PB, using the binary (1024-based) convention operating systems actually use.
- Uptime and SLA Downtime CalculatorTurn an uptime percentage like 99.9% into the downtime it allows per year, month, week and day.
- Download Time CalculatorEstimate how long a file will take to download or upload at a given connection speed, allowing for real-world overhead.
- PX to REM ConverterConvert pixels to rem and rem back to pixels for any root font size, with the CSS value ready to copy.
- Aspect Ratio CalculatorFind the aspect ratio of any width and height, and work out the matching height when you resize to a new width.
- Cloud Storage Cost Calculator: Amazon S3 vs Cloudflare R2Estimate your monthly object-storage bill on Amazon S3 and Cloudflare R2 from storage, downloads and requests, and see how much egress fees add.
- Password Entropy CalculatorMeasure the strength of a randomly generated password in bits of entropy, and see how long it would take to guess at different attack speeds.
- Cron Expression ExplainerPaste a cron schedule to read it in plain English, see the next run times, and check how often it will fire before it goes to production.
- IP Subnet Calculator (IPv4 CIDR)Enter an IPv4 address and CIDR prefix to get the network and broadcast addresses, usable host range, subnet mask, wildcard mask and host count.
- chmod Calculator: Linux File PermissionsConvert Linux file permissions between numeric (755) and symbolic (rwxr-xr-x) form, see who can do what, and get the chmod command.
- Timezone Meeting PlannerCompare working hours across several timezones at once and find the windows that actually overlap.