Everything you need for calculations

Which calculator do you need?

These fall into four groups, and the useful question is usually not which one computes the number but which one states the assumption you care about.

Borrowing and repayment

Loan and EMI both amortize a fixed-rate balance into equal payments; EMI is the same arithmetic under the name used across South Asia. Mortgage adds the parts of a housing payment that are not the loan. Each page shows the formula it used and what it assumed about the rate.

Take-home pay

Paycheck estimates US take-home pay from gross, using federal brackets, the standard deduction and FICA. It states the tax year it used and links the IRS and SSA publications the figures came from, because that is the part that goes out of date.

Everyday percentages

Percentage covers all the usual directions at once — what is X% of Y, X is what percent of Y, and percentage increase or decrease. Tip and Discount are the two specific cases common enough to deserve their own page, with splitting and sales tax built in.

Dates and ages

Date Difference measures the span between two dates in days, whole weeks, weekdays or days remaining. Age answers the related but different question of how old someone is on a given day, which is not simply the number of days divided by 365.

Health and study

BMI reports adult body mass index with the CDC category, and says plainly that BMI is a population screening measure rather than a diagnosis. GPA computes a weighted grade point average and states the scale it applied, since scales vary by institution.

How to read these results

I build and maintain these calculators myself. I am a developer, not an accountant, a lender or a clinician, so what each page offers is traceability rather than advice: the formula it used, the assumptions it made, and the published source the figures came from. You can check all three.

• Every page states its formula. The worked examples on each calculator are produced by running the calculator itself, not typed in beside it, so they cannot drift away from what the tool actually does.
• Assumptions are listed, because they are where the difference lives. Two mortgage calculators disagreeing usually differ on what they assumed about taxes, insurance or compounding — not on the arithmetic.
• Tax and statutory figures have a year on them. Brackets, standard deductions and contribution limits change annually. The paycheck calculator names the year it used and links the source; if that year is behind, treat the result as historical.
• An estimate is not a quote, a payslip, or a diagnosis. A lender’s offer, an employer’s payroll run and a clinician’s assessment all take in things these pages never see. Check anything consequential against the actual record.
• Nothing you type is sent anywhere. The arithmetic runs in your browser, so salary, loan balances and dates of birth stay on your device.

Corrections are welcome and get published: how I handle them is on the corrections policy, and the wider account of editorial practice is on the editorial policy.