Methodology

Who does this work

Calcz is run by one person. No doctor, dietitian, financial adviser or registrar reviews these pages, so the checks below are about whether the arithmetic and sources are right, not about what a result means for you. Read more about Calcz.

Choosing formulas

We use formulas and tables from public health bodies, financial regulators, scientific bodies and university sources, and we read each source on its own page before citing it. We prefer those over other calculator sites. When there is more than one accepted method, we say which one we use and why.

Calculator by calculator

Each calculator page has the full formula, a worked example and links to its sources.

Academic calculators

• Weighted Grade Calculator. A weighted mean: each grade times its weight, divided by the total weight. Shown to one decimal place.
• Final Grade Calculator. The weighted grade formula solved for the final. The version for a final that replaces your lowest test is our own algebra, set out on the page. Rounded up to one decimal place, so the score shown is always enough.
• International Grade to GPA Converter. No formula. It looks your grade up in tables published by US universities, converts the letter with standard quality points, and shows the lowest and highest result.
• GPA Calculator. Quality points divided by credits, using tables published by university registrars. Shown to two decimal places.
• Cumulative GPA Calculator. Total quality points divided by total credits. Shown to two decimal places, and the GPA needed next term is rounded up so that it’s always enough.

Fitness calculators

• BMI Calculator. The US Centers for Disease Control and Prevention formulas and adult categories. Shown to one decimal place, and the category is read from that rounded figure.
• Calorie Calculator. The Mifflin-St Jeor equation for calories at rest, with activity levels from FAO/WHO/UNU and the US National Institutes of Health. Calories at rest are rounded to a whole number, and daily targets to the nearest 10.
• Macro Calculator. Splits that stay inside the US Dietary Guidelines ranges, with calories per gram from the USDA. Rounded to whole grams.

Finance calculators

• Compound Interest Calculator. The standard compound interest formula, applied month by month with deposits at the end of each month. Calculated at full precision and shown to the cent. It leaves out taxes, fees and inflation.

Science calculators

• Molar Mass Calculator. The sum of the abridged standard atomic weights in the 2024 IUPAC table. Shown to three decimal places. Elements with no standard weight in that table are rejected instead of being filled in from elsewhere.

Testing

The calculation behind every calculator is kept apart from its interface and has its own automated tests. They cover worked examples, including figures published by a source where one exists, and edge cases such as empty fields, zero, negative numbers, very large values and text that isn’t a number.

Rounding

Rounding is listed for each calculator above. We round up when a result tells you what you need to score, because rounding down could leave you just short. Letter grades and BMI categories can change at a cut-off, so a result close to one is worth checking with your school or doctor.

Estimates

Some results are estimates, and we label them that way. There is no official universal grade conversion, so the International Grade to GPA Converter shows a range. Calorie and macro targets are starting points, because individual needs vary. Compound interest results assume the same rate every year, which real investments don’t guarantee.

Corrections

When we fix an error, we update the “Last updated” date on the calculator page. If you think a result is wrong, please tell us.