Age Calculator

Age Calculator measures the calendar difference between Birth date and Calculate age on. When analyzeAge is ready, the page shows completed years, months, and days; total months; total days; total weeks; next birthday with remaining days and a progress bar; upcoming milestone ages from MILESTONE_AGES; and long weekday names for both dates. totalHours is computed as totalDays × 24 in the helper but is not shown in AgeCalculator.jsx.

There is no file picker. Results are informational calendar math, not an official age, identity, or eligibility determination.

Both fields are type="date" (YYYY-MM-DD). Birth date defaults to empty; the comparison date defaults to today on the device. Use today only updates Calculate age on. Dates are not IANA time zones and not Unix timestamps.

parseDateValue returns null for empty or NaN Date. The helper does not set its own min/max year; the native date control’s range and UI vary by browser.

Years / months / days

diffYMD: subtract Y/M/D; if days < 0, borrow the previous month’s daysInMonth length; if months < 0, borrow a year.

Total days

totalDaysBetween: local calendar midnights, Math.floor((end − start) / 86400000). Matching dates → 0 (not “including today”).

Total weeks

Math.floor(totalDays / 7).

Total months

age.years * 12 + age.months (not totalDays / 30).

This is anniversary-style calendar subtraction, not mean-year estimates. End-of-month borrowing uses the actual previous month length from new Date(year, monthIndex + 1, 0).

nextBirthdayDate builds this year’s anniversary as new Date(asOfYear, birthMonth, birthDate). If that Date is on or after as-of, it is used; otherwise the next year. A birthday on the comparison date yields daysUntilNextBirthday === 0 and the UI “Today!”.

For February 29 births, a non-leap as-of year makes JavaScript normalize Feb 29 to March 1 when constructing that anniversary. That March 1 convention is this Date implementation, not a legal leap-day rule. birthdayYearProgress uses a 365-day assumption: 100% if remaining days are 0, else round(((365 − remaining) / 365) * 100), clamped 0–100. It is not an exact tropical year.

Milestones: ages 13, 16, 18, 21, 30, 40, 50, 65, 100 that are greater than current completed years, first four only. addYearsToDate uses the same Date constructor (leap-day roll applies). Empty list copy: “No upcoming milestone ages in the preset list for this birth date.”

1. Enter Birth date (type="date"). There is no Calculate button; useMemo runs analyzeAge(birthDate, asOfDate) whenever either field changes. Empty birth date leaves ready false and shows “Enter a birth date to calculate age.”
2. Optionally edit Calculate age on. It starts at getTodayValue() (device local YYYY-MM-DD). Dates are not IANA zones and not Unix timestamps.
3. Click Use today to set Calculate age on to getTodayValue() and clear copy flags. It does not change Birth date.
4. When ready, read Exact age, Total months, Total weeks, Total days, Next birthday (or “Today!”), and Upcoming milestone ages. Age summary repeats Exact age, Total months, Total weeks, and Total days.
5. Read Zodiac (optional) and Generation (optional) under Optional labels. The panel states they are fixed coded ranges, not scientific, legal, or official classifications.
6. Click Copy exact age to write formatAgeLabel (“N years, N months, N days”). The button reads Age copied for 1.5 seconds. These buttons render only when result.ready.
7. Click Copy full summary to write formatAgeSummary (includes both YYYY-MM-DD values, totals, next birthday, zodiac, and generation). The button reads Summary copied for 1.5 seconds. Clipboard failure is silent.
8. Click Reset calculator to clear Birth date, restore Calculate age on to today, and clear copy flags. There is no undo, download, print, or file import.

Optional labels appear only after a successful calculation. getZodiacSign(month, day) walks a fixed Western tropical table (Capricorn through Sagittarius, then Capricorn again after Dec 21). February 29 falls in Pisces on that table (before March 20).

getWesternGeneration(year): ≥2013 Alpha, ≥1997 Z, ≥1981 Millennial, ≥1965 X, ≥1946 Baby Boomer, ≥1928 Silent, else Greatest Generation. Other published tables differ. The UI states these are not scientific, legal, or official classifications.

• Identity, official birth records, or document authenticity.
• Legal age, age-restricted eligibility, school/employment/immigration/insurance rules.
• Medical, developmental, pregnancy, or lifespan status.
• Time-zone conversion of a birthday clock, or Unix epoch conversion.
• Download, print, or a shareable result URL.

A calculated result is informational. It does not verify identity, legal age, age-restricted eligibility, medical or developmental status, or an official birth record.

analyzeAge runs in the browser. Dates are not POSTed to an age API. FileWorkflowShell privacy copy says birth and comparison dates are not uploaded. trackToolEvent fires tool_started when a birth date is first entered and tool_success once when ready—payload is { tool: "age-calculator" } only, not the dates, age, zodiac, or generation. That is still first-party analytics metadata. Site assets, ads, clipboard, extensions, and shared devices remain outside this helper.

• Confirm both YYYY-MM-DD values and that as-of is the date you meant (today vs a form deadline).
• If totals disagree with another site, compare local-midnight day counts vs “including today” and UTC-only parsers.
• If the person was born Feb 29, read next birthday as this tool’s Date-normalized anniversary (often March 1 in non-leap years).
• Treat the progress bar as a 365-day sketch, not an exact year fraction.
• Ignore zodiac/generation for any official purpose.
• Copy the label or summary; keep your own record if you need a file.

• Time Zone Converter — when you need a civil clock in a listed IANA city. This calculator uses device-local calendar dates only and does not convert a birthday into another zone.
• Timestamp Converter — when the input is Unix seconds or milliseconds, not a YYYY-MM-DD birth date.