Articles
Guides and tutorials covering text, data, developer tools, and real estate investing. Each one is paired with a free browser-based tool.
Text & Writing
How to Remove Duplicate Lines from Text
Duplicate lines show up constantly when merging lists, exporting data, or combining files. Here's how to clean them quickly.
What Is Lorem Ipsum and Why Do Designers Use It?
"Lorem ipsum dolor sit amet..." has been the default placeholder text for over 500 years. Here's where it comes from and why it's still the best option.
Data & JSON
How to Validate JSON (And Fix Common Errors)
A single misplaced comma or missing bracket can break your entire application. Here's how to validate JSON and understand the most common errors.
How to Format JSON for Readability
Raw JSON is often compressed into a single line. Formatting it with consistent indentation makes debugging and reviewing far easier.
Developer Tools
How to Escape HTML Characters (And Why It Matters)
Displaying user-generated content without escaping HTML special characters is one of the most common causes of XSS vulnerabilities. Here's how to do it right.
How to Create SEO-Friendly URL Slugs
A slug is the human-readable part of a URL. Clean, consistent slugs improve readability, shareability, and search engine rankings.
What Is Base64 Encoding? How It Works and When to Use It
Base64 converts binary data into printable ASCII text. Here's how the encoding works, why it's used in emails, APIs, and data URLs, and how to decode it.
How URL Encoding (Percent-Encoding) Works
URLs can only contain certain characters. Percent-encoding converts spaces and special characters into a format safe for transmission. Here's how it works and when to apply it.
What Is a JWT? JSON Web Tokens Explained
A JWT is a compact, URL-safe token used for authentication and data exchange. Here's how the three-part structure works, what each part contains, and how to inspect one.
How to Use Regex: A Practical Guide to Regular Expressions
Regular expressions let you match patterns in text with precision. Here's the core syntax, the most useful patterns, and how to test and debug your expressions.
What Is HEIC? Apple's Photo Format Explained
HEIC is Apple's default photo format on iPhone and iPad. It's up to 50% smaller than JPEG but not universally supported. Here's what HEIC is and how to convert it.
WebP vs JPG vs PNG: Which Image Format Should You Use?
Choosing the wrong image format can double your page load time. Here's when to use WebP, JPG, and PNG — and why WebP is usually the best choice for the web.
How to Compress Images for the Web Without Losing Quality
Large images are the single biggest cause of slow websites. Here's how lossy and lossless compression work, what quality settings to use, and how to batch-optimize your images.
Real Estate
What Is Cap Rate and How Do You Calculate It?
Cap rate is one of the most widely used metrics in real estate investing. Here's what it measures, how to calculate it, and when to use it.
How to Calculate Cash Flow on a Rental Property
Cash flow is the single most important number for rental property investors. Here's how to calculate it accurately and avoid the most common mistakes.
What Is Cash-on-Cash Return and How Do You Calculate It?
Cash-on-cash return measures how much your actual cash investment earns each year. It's a more practical metric than cap rate for financed properties.
What Is the BRRRR Method in Real Estate?
BRRRR (Buy, Rehab, Rent, Refinance, Repeat) is a real estate investing strategy designed to recycle capital across multiple properties. Here's how it works.
How Much House Can I Afford?
Lenders will approve you for more than you should spend. Here's how to calculate what you can realistically afford using the 28/36 rule and the full cost of ownership.
What Is DSCR? Debt Service Coverage Ratio Explained
DSCR (Debt Service Coverage Ratio) is how lenders decide if a rental property qualifies for a loan. Learn the formula, what counts as a good DSCR, and how to improve it.
What Is the 1% Rule in Real Estate?
The 1% rule is the fastest way to screen rental properties for cash flow potential. Here's how it works, when it applies, and when to look past it.
Should I Rent Out My House or Sell It?
Renting vs. selling depends on your cash flow, equity, tax situation, and future plans. Here's a framework for comparing the two scenarios with real numbers.
How to Budget a House Flip Rehab
Underestimating rehab costs is the most common way fix-and-flip deals go wrong. Here's how to build a line-item budget and use the 70% rule to validate your offer.
How Much Are Closing Costs for Buyers and Sellers?
Closing costs catch many buyers and sellers off guard. Here's a breakdown of what each side pays, what's negotiable, and how to estimate your total before closing day.
What Is Net Operating Income (NOI) in Real Estate?
NOI is the most important number in rental property analysis. It drives cap rate, property value, and loan qualification. Here's the formula, what to include, and what to leave out.
What Is House Hacking and How Does It Work?
House hacking means living in one unit of a multi-unit property and renting out the others — often covering most or all of your mortgage. Here's how to analyze a deal and get started.
Personal Finance
How Compound Interest Works
Compound interest is the most powerful force in personal finance. Here's how it works, how to calculate it, and how to make it work for you instead of against you.
How to Pay Off Credit Card Debt Faster
Minimum payments are designed to keep you in debt for years. Here's how credit card interest actually works and the strategies that get you out faster.
How to Calculate Your FIRE Number
The FIRE number is the portfolio size you need to retire and live off investment returns indefinitely. Here is how to calculate it and what affects it.
What Is Coast FIRE and How Do You Calculate It?
Coast FIRE means you have enough invested today that it will grow to your retirement number without another dollar of contributions. Here is how to find your coast number.
Debt Snowball vs. Debt Avalanche: Which Strategy Is Better?
Both strategies pay off debt faster than minimums alone, but they work differently and produce different results. Here is how to choose.
How Much Should You Have in an Emergency Fund?
The standard rule is three to six months of expenses, but the right amount depends on your income, job stability, and financial cushion.
What Is APY and How Is It Different from APR?
APY reflects what you actually earn after compounding; APR is the raw stated rate. The difference matters when comparing savings accounts and loans.
What Is a CD Ladder and How Do You Build One?
A CD ladder splits your savings across CDs with staggered maturity dates, giving you higher yields without locking up all your money at once.
How Investment Fees Quietly Drain Your Returns
A 1% expense ratio sounds trivial. Over 30 years, it can consume 20 percent or more of your final portfolio balance. Here is the math.
What Is the Rule of 72?
The Rule of 72 lets you estimate how long it takes to double your money with a single division. It also works in reverse, and for debt.
What Is a Required Minimum Distribution (RMD)?
RMDs are mandatory annual withdrawals from tax-deferred retirement accounts, starting at age 73. Here is how they are calculated and what happens if you miss one.
How to Calculate Your Net Worth (And What It Actually Tells You)
Net worth is assets minus liabilities. It is the most complete single-number summary of your financial position, but the trajectory matters more than the number itself.
How a 529 College Savings Plan Works
A 529 plan lets your college savings grow tax-free. Here is how contributions, investment options, and withdrawals work.
What Is a Savings Rate and Why It's the Key to Financial Independence
Your savings rate — the percentage of income you save — is the single biggest lever in how quickly you reach financial independence. Here's how to calculate it and what different rates mean for your timeline.
Business
What Is Break-Even Analysis?
Break-even analysis tells you exactly how many units you need to sell before you start making money. Here's how to calculate it and use it to make better business decisions.
What Is Profit Margin and How Do You Calculate It?
Revenue is vanity, profit is sanity. Here's how to calculate gross, operating, and net profit margin, and why margin matters more than top-line revenue.
How to Calculate ROI (And When to Use It)
ROI is one of the most widely used metrics in business and investing. Here's the formula, how to apply it, and when other metrics give you a clearer picture.
How PayPal Fees Work for Sellers
PayPal's Goods and Services fee is 3.49% + $0.49 per transaction. Here's what that means for your pricing, and how to calculate the gross amount to charge so you receive what you need.
How Amazon FBA Fees Work (and How to Calculate Your Profit)
Amazon FBA involves referral fees, fulfillment fees, and storage costs that can quietly consume most of your margin. Here's how to model all of them before you source a single unit.
How to Set Your Freelance Hourly Rate
Most freelancers undercharge because they price based on what feels acceptable, not what they actually need to earn. Here's the formula to find your minimum viable rate.
How to Charge Late Fees on Unpaid Invoices
A documented late fee policy is one of the most effective ways to get paid on time. Here's how to set one up, what rates are common, and how to calculate what you are owed.
What Is Churn Rate and How Do You Calculate It?
Churn rate measures how quickly you lose customers. Even a small difference in monthly churn leads to dramatically different outcomes over time. Here's the formula and what it implies.
What Is MRR and ARR? A Plain-English Guide
MRR and ARR are the two most cited revenue metrics in subscription businesses. Here's what they measure, how to calculate them correctly, and the four components that drive MRR changes.
What Is Customer Lifetime Value (LTV)?
LTV defines how much you can rationally spend to acquire a customer. Here's the formula, how to use the LTV:CAC ratio, and the levers that move LTV over time.
What Is Customer Acquisition Cost (CAC)?
CAC is how much it costs you to acquire one paying customer. Here's what to include in the calculation, how to interpret your LTV:CAC ratio, and why CAC tends to rise as you grow.
Gross Profit vs. Net Profit: What's the Difference?
Gross profit and net profit both appear on income statements but measure very different things. Here's what each one tells you, and why high gross margin doesn't always mean profitability.
What Is Contribution Margin and Why Does It Matter?
Contribution margin shows how much each sale contributes toward covering fixed costs. It's the right metric for pricing decisions, product mix analysis, and understanding your break-even point.
How Real Estate Commission Splits Work
A 5% commission on a $400,000 home is $20,000, but it doesn't all go to one agent. Here's how commission flows from the seller through brokerages to individual agents.
How to Price a Product: Cost-Plus, Margin & Value-Based
Three pricing methods compared: cost-plus, target margin, and value-based. Learn when to use each, how to calculate your price, and how to avoid leaving money on the table.
How to Calculate Profit Per Unit Sold
Many sellers undercount their per-unit costs and end up with profit margins that look healthy but disappear in practice. Here's how to model every cost that touches each sale.
How to Find the Minimum Viable Price for Your Product
Every product has a price floor below which you lose money regardless of volume. Here's how to calculate your breakeven price and use it to make smarter pricing and channel decisions.
What Is Inventory Turnover and Why Does It Matter?
Inventory turnover tells you how efficiently you manage stock. Slow-turning inventory ties up cash, increases storage costs, and raises obsolescence risk. Here's how to calculate and improve it.
How eBay Fees Work for Sellers (And How to Calculate Your Profit)
eBay's final value fee varies by category and can reach 15% or more. Here's a breakdown of every fee sellers pay, how they stack up, and how to model your net profit before listing.
How Stripe Fees Work for Online Businesses
Stripe charges 2.9% + $0.30 per transaction for standard card payments, but fees vary by product, country, and card type. Here's what you actually pay and how to factor it into your pricing.
How Etsy Fees Work for Sellers
Etsy charges a $0.20 listing fee, a 6.5% transaction fee, and a payment processing fee on every sale. Here's how they add up and what you actually keep after each transaction.