Guides to online calculators

The reasoning behind the numbers — how each calculation works, which formula it uses, and where the result stops being reliable.

Loans and credit Budgeting and saving Percentages and tax Health calculators Everyday money

15 guides

A shopper comparing two similar cereal boxes side by side in a supermarket aisle.

Unit Prices: Compare Supermarket Costs with Online Calculators

Learn how to compare supermarket unit prices, spot misleading shelf labels, and decide when a bigger pack, multibuy or concentrate saves you money.

Everyday money 8 min read

Four people sitting around a restaurant table with plates, glasses and a folded bill holder in the centre.

Splitting the Bill with Online Calculators: Equal or by Item

Learn when to split a restaurant bill equally, when to pay only for what you ordered, and how to handle shared wine and service charges fairly.

Everyday money 8 min read

A close-up of folded banknotes and coins left beside a paper restaurant receipt on a wooden table.

Tipping Around the World: A Practical Guide with Online Calculators

Learn when, where and how much to tip in restaurants worldwide, and use free online calculators to split a bill and check a service charge before you pay.

Everyday money 8 min read

A kitchen scale on a wooden counter with uncooked lentils, eggs and a salmon fillet arranged beside it.

Macros Explained: Protein, Carbs, Fat and Online Calculators

A plain guide to turning macro percentages into grams, why protein matters most, and what online calculators can and cannot tell you.

Health calculators 8 min read

A wooden kitchen counter with a glass of water, a notebook, a pen, and a small bowl of nuts and fruit arranged for meal planning.

Daily Calorie Needs: What Online Calculators Get Wrong (and Right)

Learn how daily calorie calculators estimate your needs, why the number drifts over time, and when to see a dietitian rather than trust a formula.

Health calculators 8 min read

A fabric tape measure lies loosely coiled next to a simple digital scale on a pale wooden floor in soft daylight.

What BMI Can and Cannot Tell You: Online Calculators Explained

BMI is the world’s most-used weight number, but it is not a diagnosis. Learn the formula, the band limits, who it misclassifies, and a more useful second check.

Health calculators 8 min read

A paper invoice, pen and small calculator on a wooden desk under soft natural light.

Adding and Removing VAT: A Plain Guide for Online Calculators

Learn how to add and remove VAT correctly: why you divide by 1 + rate, the four-unit mistake, and the margin-versus-markup trap on the same invoice.

Percentages and tax 8 min read

A supermarket shelf showing two different pack sizes of the same product with price labels underneath.

Sale Maths: Online Calculators for Stacked Discounts and Real Savings

Learn how retailers phrase discounts so you can check the real saving instantly with online calculators and unit-price comparisons.

Percentages and tax 8 min read

A wooden desk with a notebook, a basic calculator, a pen and a coffee cup, seen from above in soft daylight.

Percentage Calculations Explained: Online Calculators and Four Sums

Learn the four percentage calculations everyone confuses, with worked examples and formulas so you pick the right base every time.

Percentages and tax 8 min read

A notebook, pen and small stacks of euro coins arranged on a wooden desk next to a printed savings tracker.

Plan a Savings Goal That Actually Arrives with Online Calculators

Use online calculators to turn a vague goal into a date: months-to-goal formulas, annual-cost traps and interest over different horizons.

Budgeting and saving 8 min read

A small stack of euro notes and a household budget notebook on a plain kitchen table, lit by soft morning window light.

How Big Should Your Emergency Fund Be? Use Online Calculators to Check

Find your real essential monthly spending with online calculators, set a months-of-expenses target, and learn where to keep your emergency fund.

Budgeting and saving 8 min read

A person reviewing printed bank statements and a notebook on a kitchen table with a cup of tea and a calculator nearby.

50/30/20 Budget Rule: What Online Calculators Can and Cannot Show

The 50/30/20 rule splits after-tax income into needs, wants and savings, but percentages can mislead when rent or debt is high. This is an honest guide.

Budgeting and saving 8 min read

A person comparing two printed loan quotes side by side at a kitchen table with a calculator and a cup of coffee.

APR vs Interest Rate: Compare with Online Calculators

We explain what APR and interest rate really mean, why identical rates can cost different amounts, and when APR itself misleads.

Loans and credit 8 min read

A person sits at a kitchen table with a laptop, a notebook, a pen and a house key, reviewing papers in warm window light.

Using Online Mortgage Calculators Without Fooling Yourself

Learn what online mortgage calculators leave out, how the standard repayment formula actually works, and how to compare the true cost of any home loan.

Loans and credit 8 min read

A tidy desk with a tablet showing a repayment schedule, a notepad and a pair of reading glasses under soft natural light.

How Loan Interest Works: A Practical Guide Using Online Calculators

Learn how loan interest, amortisation and term length affect total cost. Use browser-based online calculators to test numbers before seeing a lender.

Loans and credit 8 min read