Guides
Money explained in plain English.
Short, practical guides to the everyday money questions — what your payment really covers, how interest stacks up, and how to decide. Each one is backed by a free calculator.
What Is a Dollar From the Past Worth Today?
A 1990 dollar and a 2024 dollar are not the same dollar. Here is how to convert between any two years, and what the numbers actually mean.
Read guideHow to Add a Fundraising Thermometer to Your Website
Show donors the progress toward your goal with a live thermometer you can paste onto any web page in one line of HTML.
Read guideHow to Find Out What Your Subscriptions Really Cost
The $9.99 charges are not the problem. The problem is that you have eleven of them. Here is how to see the real total and act on it.
Read guideHow to Compare Unit Prices and Spot the Better Deal
The big box is not always the better buy. Here is how to compare cost per unit across different pack sizes in seconds.
Read guideHow to Calculate Your Break-Even Point Step by Step
Divide fixed costs by the contribution margin per unit to find how many units you must sell to cover all your costs.
Read guideHow to Calculate Commission: Flat, Tiered, and Base Pay
Multiply the sale by the commission rate for flat plans, or apply each tier band separately for tiered commission.
Read guideHow to Calculate Your Debt-to-Income Ratio (DTI)
DTI compares your monthly debt payments to your gross income, and this guide shows the front-end and back-end math.
Read guideHow to Calculate Straight-Line Depreciation (With Example)
Subtract salvage value from cost and divide by the asset's useful life to find annual depreciation.
Read guideHow Much to Charge as a Freelancer (Set Your Rate)
Divide your target income plus expenses by the hours you can actually bill to find your rate.
Read guideHow to Calculate GST (Add It or Take It Off a Total)
How to add and remove GST, plus the current rates for Australia, New Zealand, Singapore, Canada and India.
Read guideHow to Calculate Profit Margin (With a Worked Example)
The profit margin formula, a worked example, and how margin differs from markup.
Read guideHow to Calculate Markup (Formula and Worked Example)
The markup formula, a worked example, and how to convert markup into margin.
Read guideHow to Calculate Your Net Worth (Assets Minus Debts)
Net worth is everything you own minus everything you owe, and this guide walks through both sides of the math.
Read guideHow to Calculate Overtime Pay (Time and a Half Made Simple)
Multiply your hourly rate by 1.5 to get your overtime rate, then add it to your regular pay.
Read guideHow to Calculate a Pay Raise (Percentage and New Salary)
Multiply your old salary by one plus the raise percentage to find your new pay.
Read guideHow to Calculate ROI with a Simple Formula and Example
Subtract the cost from the gain, divide by the cost, and multiply by 100 to get your return on investment as a percentage.
Read guideHow the Rule of 72 Works (Doubling Your Money Fast)
Divide 72 by your interest rate to estimate the years it takes an investment to double, no calculator required.
Read guideHow to Calculate Selling Price from Cost and Margin
Divide your cost by one minus the target margin to set a selling price that actually hits the margin you want.
Read guideHow to Work Out VAT (Add It or Strip It Back Out)
The exact arithmetic for adding 20% VAT to a net price and for working backwards from a gross price.
Read guideWhat Is a Valid Example IBAN (and How to Generate One)
Need a sample IBAN to fill a form or test some code? Here is what makes an IBAN valid on paper, and how to generate one safely.
Read guideHow to Build an IBAN From a Bank Code and Account Number
An IBAN is just your country, bank code, account number and two check digits. Here is how those check digits are worked out.
Read guideHow to Check a German Bank Account Number
Every German account number has a check digit. Here is what it is for and how to confirm a number is internally consistent.
Read guideHow to Find a Bank's BIC From Its Bank Code
A BIC identifies the bank; the IBAN identifies the account. Here is how to find the BIC for a German bank.
Read guideHow to Check if an IBAN Is Valid
An IBAN has a built-in checksum that catches almost any typo. Here is how the check works and how to read each result.
Read guideAPR vs Interest Rate: What's the Real Cost of a Loan?
The interest rate sets your payment; the APR reveals the true cost. Learn why they differ and how to compare loans fairly.
Read guideHow to Work Out a Car Payment Before You Buy
The sticker price isn't the payment. See how trade-in, tax and fees roll into the loan and what it really costs each month.
Read guideHow a Certificate of Deposit Pays Out
A CD trades access for a guaranteed return. See how APY drives the payout and when locking up your money is worth it.
Read guideHow Compound Interest Grows Your Savings
Compound interest is interest earning its own interest. See why starting early beats saving more, and how to model your own growth.
Read guideHow Long Will It Take to Pay Off Your Credit Card?
Paying the minimum can keep a card alive for a decade. See what your balance really costs and how a fixed payment clears it.
Read guideSnowball vs Avalanche: The Fastest Way Out of Debt
Two strategies, one goal. Learn how snowball and avalanche differ, and which clears your debts faster — or keeps you motivated.
Read guideHow to Calculate a Discount and Stacked Sale Prices
Find the real sale price fast — and learn why 25% off then 10% off isn't 35% off, but something a little less.
Read guideHow Much Should You Put Down on a House?
Why 20% down matters, what PMI costs you, and how to decide between a bigger down payment and keeping cash in reserve.
Read guideHow to Estimate Your Federal Income Tax
Tax brackets confuse almost everyone. Learn how marginal rates really work and why a raise never lowers your take-home pay.
Read guideHow Inflation Eats Away at Your Money
Inflation works in two directions: prices climb and cash loses value. See what that does to your money over a decade or two.
Read guideHow to Measure Your Real Investment Return
A 100% gain sounds great — but over how long? Learn why CAGR is the honest way to compare investment returns.
Read guideHow Loan Payments and Interest Actually Work
Understand what sets your monthly loan payment, and why a longer term lowers the payment but raises the total you pay.
Read guideHow to Calculate Your Monthly Mortgage Payment
Break a mortgage payment into its real parts — principal, interest, taxes and insurance — and see why early payments are mostly interest.
Read guideHow to Calculate Percentages (Three Common Ways)
Three percentage questions cover almost everything: a share of a number, a ratio, and a change. Learn the quick method for each.
Read guideWhen Does Refinancing a Mortgage Actually Pay Off?
A lower payment isn't always a better deal. Learn the break-even point and how to tell a real refinance win from a costly one.
Read guideHow to Estimate What You'll Have at Retirement
Turn your current savings and monthly contributions into a retirement projection, and see what income it could realistically support.
Read guideHow to Convert Hourly Pay to Annual Salary
Convert between hourly, weekly, monthly and annual pay — and know why gross figures aren't what lands in your account.
Read guideHow to Add or Remove Sales Tax from a Price
Add tax to a price, or pull the tax back out of a total. Two quick calculations that come up more often than you'd think.
Read guideHow to Hit a Savings Goal by a Set Date
Have a number and a deadline? Work backwards to the monthly amount you need to save, with interest doing part of the work.
Read guideHow to Calculate a Tip and Split the Bill
How much to tip, how to do it in your head, and how to split the total fairly across the table — without the awkward math.
Read guideSkip the reading — just run the numbers
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