Math & Finance Tools.

Financial calculators and math tools fill a specific gap: they are faster than spreadsheets for one-off calculations, more accurate than mental arithmetic, and more transparent than mobile apps that show a result without explaining how they got there. Every calculator here shows its work, which is the difference between getting a number and understanding a number.

The loan and mortgage calculators illustrate this particularly well. You enter the principal, interest rate, and term, and you get not just the monthly payment but the full amortization schedule showing how each payment splits between interest and principal over time. In the early months of a mortgage, the majority of each payment goes to interest. The calculator makes this concrete, which helps you understand why making extra principal payments early in a loan term has a disproportionately large effect on total interest paid.

Compound interest is one of the most misunderstood concepts in personal finance, and the calculator shows exactly why it matters. Enter 1000 euros at 7% annual interest over 30 years. The result is not 3,100 euros (30 years of 7% of 1,000) but 7,612 euros, because each year the interest earns interest. The calculator lets you compare different compounding frequencies, monthly versus annual versus daily, and see the effect of regular additional contributions, which is how pension and savings planning actually works.

VAT and tax calculations come up constantly for small business owners and freelancers. Whether you need to add VAT to a net price, extract VAT from a gross price, or calculate the effective tax rate at different income levels, the VAT and salary calculators handle these in both directions. For European users in particular, the default VAT rates for the most common countries are pre-loaded so you do not need to look them up.

Unit conversion is one of those tools where precision matters. The weight, length, and general unit converters handle the full set of SI units alongside imperial and US customary units, with enough decimal precision for scientific and engineering use. The aspect ratio calculator is specifically useful for designers and video producers who need to calculate dimensions that maintain a specific ratio, such as resizing a 1920x1080 video to 1280 pixels wide while keeping 16:9 proportions.

The BMI and calorie calculators sit at the intersection of math and health. BMI is calculated from height and weight using the standard WHO formula, with context about what each range means. The calorie calculator uses the Mifflin-St Jeor equation, currently the most accurate formula for estimating basal metabolic rate, adjusted for activity level. Both tools display results with clear explanations of what the numbers mean in practice.

Random number generators, dice rollers, coin flips, and decision wheels serve a different purpose: introducing genuine randomness into decisions where you want to avoid bias. Random sampling for quality control, selecting a winner from a list of participants, making an arbitrary choice when two options are otherwise equal, or simply rolling a D20 for a tabletop game. The tools use `crypto.getRandomValues()` for unpredictable results.