Age Calculator

Overview

The Age Calculator converts any two calendar dates into a complete, human-readable age string—covering everything from years down to seconds. Whether you are organising events, verifying age eligibility, or simply satisfying your curiosity, this tool eliminates manual calculations and potential errors.

Behind the scenes, the calculator leverages the Day.js library to produce fast and accurate results, even across leap years, different month lengths, and daylight-saving changes.

Because all processing runs locally in your browser, your dates remain private; no information is transmitted or stored on external servers. This makes the calculator perfect for sensitive use cases such as HR onboarding, legal compliance, and medical paperwork.

Designed with a responsive Bootstrap 5 interface, it adapts seamlessly to phones, tablets, and desktop screens, ensuring quick access wherever you are.

Key Features

Discover why this tiny utility punches well above its weight.

Instant breakdown — Get years, months, weeks, days, hours, minutes, and seconds at a glance.
100 % client-side — Dates never leave your browser, protecting personal information.
Next-birthday countdown — See exactly how long until the next celebration.
Responsive UI — Optimised for touch devices and desktop workstations alike.
URL parameters — Share or bookmark preset dates for quick reuse.

Formulas

The calculator uses Day.js differences under the hood; the table shows the plain-language logic.

Metric	Expression (pseudo-code)	Notes
Years	`years = diff(date₂, date₁, 'year')`	Ignores smaller units; acts as base for month refinement.
Months	`months = diff(date₂, date₁, 'month')`	Full calendar months; remainder (`months % 12`) forms month part of age.
Weeks	`weeks = diff(date₂, date₁, 'week')`	Remainder after full months (`weeks % 4`).
Days / Hours / Minutes / Seconds	`diff(date₂, date₁, unit)`	Calculated successively to avoid rounding drift.
Next Birthday	`date₁ @ year(date₂) → if past → +1 year`	Difference in days between adjusted birthday and `date₂`.

Step-by-Step Guide

Let the interface do the heavy lifting—just supply the two dates and read the results.

Pick a Date of Birth from the first calendar field.
Select an “Age at” date—default is today if you leave it blank.
Review the green banner for the full age string; the list below breaks each time unit out for precision.
Note the countdown—the “Next Birthday” row shows days left until the next milestone.

Frequently Asked Questions

Find quick answers to common queries below.

Does the calculator support leap-year birthdays?

Yes. If your birth date is 29 February, the tool adjusts to 28 February or 1 March in non-leap years to maintain accuracy.

Why are weeks and months shown separately?

Months vary from 28 to 31 days, so breaking them out avoids misinterpretation and keeps the output intuitive.

Is my data stored or logged?

No. All calculations happen entirely in your browser. Closing the tab wipes every input.

Can I link directly to pre-filled dates?

Absolutely. The tool supports URL parameters (?date_birth=YYYY-MM-DD&date_age=YYYY-MM-DD) for sharing presets.