Using Our Tools guides

How to calculate an age gap

Find the exact age gap between two people with a step-by-step method and a free online calculator that works instantly — no sign-up required.

How to calculate percentages

Quickly find percent of a number, change, discount, markup, and tips with worked examples. Use these free, instant formulas online with no registration.

How to calculate body fat percentage

Compare DEXA, calipers, and Navy tape methods to find your body fat percentage. Get healthy ranges by age and sex with this free, no-download guide.

How to calculate overtime pay

Verify FLSA 40-hour rules, California daily OT, and double-time rates against your paycheck. Check your pay instantly with this free online method.

How to calculate TDEE and BMR

Estimate your BMR and TDEE using 5 activity multipliers in 2 minutes. Get a worked example for a 170-lb person instantly, free, and with no sign-up.

How to calculate your true hourly rate

Convert your salary to real per-hour earnings by factoring in PTO, benefits, and commute. See why $55k remote beats $65k in-office with this free online tool.

How inflation affects your savings

Free inflation impact calculator. CPI-U formula, real vs nominal return, and a 2-minute audit to spot accounts quietly losing value. No sign-up.

How to compare discounts

Instantly understand how stacked discounts compound, not add. Free, no-signup guide to BOGO math, coupon order, and unit-price comparisons.

How to calculate percentage change

Learn the percent-change formula, distinguish percentage points, and compute year-over-year growth. Get instant, free analysis online, no sign-up needed.

How to split a restaurant bill

Split a restaurant bill without stress: tip before or after tax, even vs itemized, handle shared wine and abstainers. Free online guide, no sign-up needed.

How to track ovulation

Track ovulation with four methods ranked by accuracy, symptothermal combinations, the 6-day fertile window, and when to see a clinician. Free guide.

How to boost your GPA

Calculate which credits actually move your GPA, when to retake or withdraw, and if your target is reachable. Free online method to plan instantly.

How to calculate what you need on a final

Solve (target − current) / final weight with three examples, including curve-adjusted planning. Get your required score instantly with this free online tool.

How to calculate marketing ROI

Analyze revenue, gross-profit, and contribution ROI with attribution models. Run an incrementality test with this free, no sign-up browser tool.

How to compare loan offers

Evaluate loan offers by comparing APR over interest rates to find the real total cost. Free, online lesson on prepayment penalties and red flags.

How much house can you afford

Free affordability calculator using the 28/36 rule, net-pay math, target PITI back-solve, and three stress tests before you make an offer. No sign-up.

How to project retirement with compound interest

Calculate the future-value formula, use 7% real returns, and apply the 4% withdrawal rule free online. Estimate your retirement number instantly with no signup.

How to interpret your BMI

BMI as a screening tool misused as a verdict. Interpret your BMI online for free instantly with no registration, and learn better health measures in your browser.

How to read your paycheck

Decode every line on a US pay stub — gross, deductions, FICA, YTD — and find withholding errors free online. Understand your take-home pay instantly with no signup.

How to schedule across time zones

Schedule meetings across time zones while dodging DST bugs and finding fair rotations. Instant free tool with no download needed.

How to set your macros

Calculate your macro split for cutting, maintaining, or bulking with the 80% adherence rule. Free instant tool with no sign-up required.

How to estimate your tax bill

Clarify marginal vs effective rates and uncover missed deductions like HSA and home office. Free instant guide to withholding safe harbors, no registration.

How to calculate days between two dates

Calendar, business, and trading days, inclusive/exclusive endpoints, leap years, 30/360, time-zone gotchas, ISO format tips. Free online guide. No sign-up.

How to choose snowball vs avalanche

Find the fastest debt payoff strategy by comparing snowball and avalanche methods with free, no-signup calculations inspired by the Kellogg study.

How to set a savings goal

Calculate your savings target, monthly contribution, and best account to use. Free instant planner with no registration needed.

How to convert salary to hourly rate

Calculate your hourly rate from salary online instantly. Free tool compares nominal, working, and net rates with no registration required.

How to set your freelance rate

Calculate your freelance rate by back-solving from target net income with a 5-input formula. Free, instant online tool, no sign-up.

How to track your net worth

Track your net worth accurately: learn what counts as assets and liabilities, set a quarterly cadence, and use age‑based benchmarks. Free instant guide, no sign‑up needed.

How to plan your race pace

Estimate goal pace, negative splits, and adjustments for hills, heat, and altitude free online. Plan your fueling and mental checkpoints in seconds with no signup.

How to shop for a car loan

Compare car loan numbers and avoid dealer traps with pre-approval strategies and the 20/4/10 rule. Free, instant online guide, no sign-up.

How to send a professional invoice

Generate professional invoices with the 10 must-have fields and optimal payment terms. Free, instant template, no sign-up required.

How to calculate VAT

Add or remove VAT with country-specific rates like UK 20% and Germany 19%. Understand B2B reverse charges and OSS rules online, free and instantly.

How to calculate age between two dates

Decompose years, months, and days with leap-year handling and inclusive counting. Use this instant, free calculator to check legal and biological age online.

How to calculate a tip

Quickly estimate 15-20% tips with mental math, navigate pre-tax rules, and split checks fairly. Get instant, free guidance for any country online.

How to plan for retirement

Apply the 25x rule, account priority order, and glide path online in seconds. Free retirement planning with no signup — check your savings rate now.

How to create a strong password

Generate a strong password instantly online for free. Build high-entropy passphrases following NIST 2026 rules with no download needed.

How to convert between units

Quickly convert length, weight, volume, and temperature with offset math. Free, instant guide clarifies US vs UK gallons, data sizes, and ton variants.

How to track your pregnancy week by week

Track your pregnancy week by week from LMP dating to birth: understand trimester breakdowns, appointment schedules, and normal vs concerning symptoms. Free online guide.

How to convert currency when traveling

Check exchange rates and avoid DCC traps with our free online currency converter. Instant calculations to plan your travel cash strategy, no sign-up.

How to add a watermark to a PDF

Stamp a text watermark like DRAFT or CONFIDENTIAL across every page of a PDF. Get opacity tips and access a free tool in seconds, no registration.

How to add page numbers to a PDF

Insert page numbers into any PDF by picking position, size, and format. Learn how booklets differ from contracts in this free guide with no sign-up.

How to remove metadata from a PDF

Strip author names, timestamps, and software traces from PDF files free online. Follow a privacy checklist to sanitize documents instantly with no signup required.

How to Make a Simple Invoice

Write clean, professional invoices with pricing and payment terms. Create your invoice online for free instantly, no sign-up required, and get paid faster.

How to Calculate Profit Margin

Break down gross, operating, and net profit margins with clear examples. Know which number to quote and why — free, instant, and no sign-up needed.

How to Convert Files Locally Without Uploading

Browser-only file conversion keeps your data private — no upload, no cloud, no server logs. Test if a converter is local, online vs desktop comparison

Best Free File Converters for Mac and Windows

Find cross-platform file converters for macOS, Windows, and the web instantly. Transform documents using built-in OS features or no-install online tools.

PDF to Word and Editable Text Conversion Guide

Convert PDF to Word in 30 seconds, OCR scanned and handwritten PDFs, handle complex tables and multi-column layouts. Free online guide, no signup.

Bulk and Batch File Conversion Guide

Learn three approaches to convert hundreds of files at once — from one-time sensitive jobs to recurring automation. Free online guide with no registration needed in your browser.

CSV and Spreadsheet Data Conversion Guide

Convert between CSV, JSON, XML, YAML, and Excel cleanly while avoiding auto-corruption of data like ZIP codes. Read our free guide, no registration.

Converting Files Without Losing Quality

Convert files without quality loss — lossy vs lossless, PNG/JPG/WebP/AVIF tradeoffs, metadata, compression damage. Free online guide, no signup.

File Formats You Actually Need to Know

Identify the ~20 file formats covering 95% of daily use — docs, images, data, audio, video, archives. Free reference guide, no sign-up needed.

File Converter Troubleshooting Guide

Debug failed file conversions — 6 common failure modes, slow conversions, large files over 500 MB, speed-up tips. Free online guide, no sign-up.

How File Converters Actually Work

Understand the decode-transform-encode pipeline, why some info is lost, and encrypted file limits. Free insights in one read, online with no sign-up.

Ebook and 3D File Conversion Guide

Convert PDF to EPUB, STL to OBJ, and 3MF without detail loss using free browser tools. Step-by-step guides — no download, instant access.

How to Choose a File Converter

Select the right file converter instantly by evaluating sensitivity, frequency, and fidelity needs. Free guide with a simple 5-question decision framework, no sign-up.

Common File Conversion Questions Answered

Solve recurring file conversion questions — Office to text, metadata privacy, format choices, speed, and encrypted files — with free answers online instantly.

GitHub Pages and Hosting Explained

Free guide to compare GitHub Pages vs traditional hosting, decode GitHub pricing tiers, and decide if GitHub can replace Slack or Dropbox for teams.

GitHub Public vs Private + Permissions Guide

Compare private versus public repos and understand crucial permissions for client projects and IP protection. Instantly learn to secure your code with this free guide.

GitHub vs Alternatives + Team Features

Compare GitHub with GitLab and AI-first alternatives to find the best fit for your team. Analyze features for multiple repositories and non-technical workflows instantly.

Common GitHub and Copilot Questions Answered

Solve recurring GitHub and Copilot questions — abandoned projects, offline use, finding code, forking, recovering deleted code — with free answers online instantly.