Mean, Median and Mode: Which Average Fits the Data?
Mean, median and mode all summarize a dataset, but they answer slightly different questions. Choosing the right one can prevent a misleading description of typical values.
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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 โ 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.
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Reorder Point: How to Calculate When to Buy More Stock
A reorder point turns demand and supplier lead time into a practical trigger for replenishment. It is different from inventory turnover because it answers when to order, not how quickly stock moves overall.
How to Estimate Household Water Use and Cost
Water-use estimates turn everyday activities into measurable volumes. The key inputs are flow rate, time or cycle volume, and the unit used by the water provider.
Capacity Utilization: How to Measure How Much of Your Capacity You Use
Capacity utilization compares actual output with a defined capacity. It can reveal unused production potential, but the result depends heavily on how capacity is defined.
How to Calculate Shipping Cost When Package Size Matters
Shipping cost is not always based on the scale reading. Large, lightweight packages can be charged by dimensional weight, so a useful estimate must consider both physical weight and package size.
Current Ratio vs Quick Ratio: How to Measure Short-Term Liquidity
Current and quick ratios both compare short-term assets with short-term obligations, but they do not include exactly the same assets. Understanding the difference helps explain a company's near-term liquidity position.
How Stacked Discounts Actually Work (They Don't Add Up)
Two discounts of 30% and 20% give you 44% off, not 50%. Here is the method for calculating any combination of discounts, coupons and cashback correctly.
Cost Per Use: A Simple Way to Judge Whether Something Is Worth Buying
Price tells you what something costs once. Cost per use tells you what it costs each time you use it, which is usually the more relevant number for anything you will own for years.
How AI Uses Calculations: What AI Can Estimate and What You Should Verify
AI can produce useful estimates, but it is not the same thing as a deterministic calculator. This guide explains the difference and shows where numerical verification matters.
How to Compare Decisions Using Cost, Time and Opportunity Cost
A good decision comparison puts alternatives on the same basis, includes hidden costs and time, and tests what happens when the assumptions are wrong.
How Businesses Use Numbers to Compare Costs, Margins and Cash Flow
Large businesses use the same core calculations as small businesses: revenue, costs, margins, cash flow and scenario analysis. The difference is the scale and the quality of the underlying records.
How to Calculate Whether Renting or Buying Actually Costs Less
Comparing rent to a mortgage payment leaves out most of what buying actually costs. Here is the fuller calculation, including the horizon at which buying tends to catch up.
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 โ a division, a multiplication, occasionally an exponent โ 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.