How to Calculate Your Electricity Bill From Appliance Wattage
A bill arrives as one total. Working out where it comes from starts with a single formula applied to each appliance you actually use.
Articles
Blog
Practical guides to the calculations behind everyday decisions: the formulas, worked examples, the assumptions each one makes on your behalf, and the mistakes that produce a confident-looking wrong answer.
Every article here starts from a question someone actually needs answered — what a pay rise is worth after inflation, whether the larger pack is really cheaper, how much a set of small subscriptions costs over a year, what a discount stacked on a discount actually comes to. Each one gives the formula, walks through a realistic example with numbers, and then does the part that matters most: explains where the calculation stops being reliable.
Where a calculator on this site covers the same ground, the article links to it, so you can read the reasoning first and then run your own figures. Results throughout are estimates for planning and educational purposes; rates, taxes, fees and personal circumstances change the outcome.
81 articles · Page 5 of 7
How to Calculate a Realistic Daily Travel Budget
Most trip budgets go wrong the same way: flights and hotels get planned carefully, and everything else gets a hopeful guess. Here is how to calculate the guess properly.
The Accounting Equation Explained: How Assets, Liabilities and Equity Balance
Every transaction a business makes changes at least two numbers on its balance sheet, never just one. The accounting equation is the rule that guarantees the two sides always end up equal.
How to Price a Product Step by Step (From Cost to Shelf Price)
Pricing isn't one calculation, it's four in sequence: know your full cost, decide your target margin, check it against break-even, and sanity-check it against the market.
How Much Car Can You Actually Afford? A Payment-to-Income Calculation
The loan payment a lender approves you for and the payment you can comfortably afford are often two different numbers. Here is how to calculate the second one.
How to Calculate the Monthly Savings Needed for a Financial Goal
A savings goal without a monthly number attached is just a wish. Here is how to turn a target and a deadline into the figure that actually needs to leave your account each month.
How to Calculate Your Take-Home Pay From Gross Salary
A job offer is quoted in gross salary. A budget has to run on take-home pay. Confusing the two is one of the most common reasons a new budget doesn't add up.
Total Cost of Ownership: How to Calculate the Real Cost of a Big Purchase
The price tag is where the cost of owning something starts, not where it ends. Total cost of ownership adds everything that comes after the purchase, which is often where the real difference between two options actually lives.
How to Calculate the Income You Actually Need as a Freelancer
An hourly rate answers what to charge per hour. It doesn't answer whether that rate, at your realistic billable hours, actually adds up to enough. Here is the calculation that does.
How Loan Amortization Works: Why Early Payments Are Mostly Interest
Two payments of the same size on the same loan aren't equal. Early on, most of a payment is interest; years later, most of it is principal. Understanding why explains a lot about how loans actually work.
How to Calculate Solar Panel Payback Period
A solar payback estimate is only as good as the assumptions behind it. Here is the calculation, and the inputs worth checking carefully before trusting a number.
How to Calculate the True Cost of a University Degree
Tuition is the number on the brochure. The true cost of a degree includes several other categories that, added together, are often larger than tuition itself.
How to get the most from these articles
Read the assumptions and limitations section before trusting any number for a real decision. Most of these calculations are short — a division, a multiplication, occasionally an exponent — and the arithmetic is rarely where things go wrong. What goes wrong is using a figure that does not match the situation: an advertised fuel-consumption number instead of your own, a total-spending figure where essential spending was needed, or a rate quoted on a different basis from the one you are comparing it against.
Several of the articles overlap on purpose. Percentage change, reverse percentages and stacked discounts are the same underlying idea applied to three different problems, and reading two of them together tends to make the third obvious.