Online Calculators
Precise, private calculators that run entirely in your browser — dates and ages, timesheet hours, GPA and grades, concrete volume, IPv4 subnets and unit conversion. Every date is compared using integer day counts in UTC, so results never shift with a timezone or a daylight saving change, and nothing you type is uploaded, logged or stored.
Date & Time
8 calculators
Age Calculator
Exact age in years, months and days plus total weeks, days, hours and minutes, next birthday countdown, day of the week you were born and leap days lived.
Chronological Age Calculator
Years, months and days between date of birth and an assessment date — the format required by clinical reports, psychometric scoring and school admissions.
Age Calculator on a Date
How old someone was — or will be — on any specific past or future date. Useful for eligibility cut-offs, forms, records and anniversaries.
Age Calculator Today
Enter one date of birth and get your age as of today, recomputed live in your own timezone. No second date, no settings.
Age Calculator India
Age from a DD/MM/YYYY date of birth in the format Indian forms, exams and government portals ask for, with the completed-years rule and cut-off dates.
Date Calculator
Add or subtract days, weeks, months and years from any date, or measure the span between two dates in days, weeks, months, weekdays and weekend days.
Time Calculator
Add and subtract hours, minutes and seconds, or find the elapsed time between two clock readings — including spans that cross midnight.
Hours Calculator
A weekly timesheet that totals worked hours from clock-in and clock-out times, subtracts breaks, splits overtime and multiplies by your pay rate.
Health & Family
4 calculators
Baby Age Calculator
Your baby’s age in days, weeks and months with developmental stage, plus corrected (adjusted) age for babies born preterm.
Child Age Calculator
Your child’s age in years, months, weeks and days, plus age in completed months for growth charts and school-entry cut-off dates.
Gestational Age Calculator
Gestational age in weeks and days with the estimated due date, trimester, term classification and milestone dates — from LMP, conception date or a known due date.
Dog Age Calculator
Your dog’s age in human years using the AKC size-banded chart rather than the debunked “multiply by seven” rule, with life stage and the epigenetic-clock figure.
Exam Eligibility
1 calculator
Education
2 calculators
GPA Calculator
Term and cumulative GPA on the unweighted 4.0 scale or a weighted 5.0 scale with honours, AP and IB bumps — plus the average you still need to hit a target.
Grade Calculator
Your weighted course percentage from homework, quizzes and exams, the letter grade it maps to, and the mark you need on the final to reach the grade you want.
Construction
1 calculator
Networking
1 calculator
Unit Conversion
1 calculator
Which one do you need?
One row per calculator, phrased as the question rather than the tool. The ten age tools share a single date engine, so they never disagree with each other — they differ in what they ask for and what they report.
201 reference pages
Some questions have one fixed answer and no input to give. Those get a page of their own, worked all the way through, with the matching calculator on it so you can change the numbers.
Age by birth year, 1930–2024
95 pagesOne page per birth year: the age you turn this year, the age range you are in right now, the generation the year belongs to and the day counts that go with it.
See all 95 →Named unit conversions
81 pagesThe exact factor, the formula written out, a reference table at the values people actually use and the reverse direction — across 12 measurements and 107 units.
See all 81 →IPv4 subnet masks, /8–/32
25 pagesOne page per prefix length: the mask in dotted decimal and binary, the wildcard mask, a worked block address by address, and how many fit inside a larger prefix.
See all 25 →How these calculators work
Age arithmetic looks trivial and is not. Months contain between 28 and 31 days, leap years break the multiply-by-365 shortcut, and subtracting timestamps built from local dates gives an answer that is one day out for part of the year in any timezone that observes daylight saving.
Every calculator here converts each date to an integer day number in UTC and does integer arithmetic on those numbers. Calendar ages are built by counting whole months forward from the date of birth with day-clamping — the same convention as spreadsheetDATEDIFand the JavaScript Temporalproposal — so month ends and 29 February behave correctly. The shared engine is covered by an automated test suite that asserts these edge cases on every change.
The others follow the same rule: use the definition, not a shortcut. Conversions go through one base unit against exact factors rather than a table of pairs; subnet maths is done on 32-bit integers, with the RFC 3021 /31 and /32 cases handled instead of a blanket “minus two”; grades and GPA are weighted sums with the target-mark algebra solved rather than guessed. Each calculator shows the formula it applied, so the answer can be checked instead of trusted.
Read the full method on the age calculator →Common questions
Are these calculators free?
Yes, all of them, with no account, no sign-up and no usage limit. They are plain web pages with client-side JavaScript.
Is anything I type sent to a server?
No. Every calculation here runs in your browser. Dates of birth, timesheets, grades, IP addresses and exam details are never uploaded, never logged and are not written to cookies or local storage.
Do they work offline?
Once a page has loaded, yes. The arithmetic needs no network access, so a calculator keeps working if your connection drops.
Why are there several age calculators instead of one?
Because the questions are genuinely different. An assessment report needs years, months and days at a specific test date; a newborn is measured in weeks and may need corrected age; a pregnancy is measured in weeks plus days from the last menstrual period; UPSC eligibility turns on age at a fixed 1 August cut-off; and a dog’s age has to be converted by size band. Each page is built for its own question, and all ten share one date engine so they never disagree.
What are the reference pages?
Pages that answer one fixed question completely rather than taking input — the age for a given birth year, a single unit conversion with its factor and reference table, or one subnet prefix worked through end to end. There are 201 of them, and each carries the matching calculator so you can change the numbers.
Which calculator should I use for a work timesheet?
The hours calculator. It takes clock-in and clock-out times for a week, subtracts unpaid breaks, splits hours over your overtime threshold and multiplies by a pay rate. The time calculator is for arithmetic on durations and clock readings rather than for a timesheet.
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