| Metric | Value | Copy |
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Chronological age measures how long you have been alive from the instant of birth to a specific target moment. Families, compliance teams, and planners rely on that figure to manage milestones, eligibility, and benefits. Calculating it precisely prevents mistakes that arise when mental math spans leap years or mixes local and international date formats.
Enter your birth date, optional birth time, and the date or time you care about, and the calculator returns a readable breakdown of years, months, days, hours, minutes, and seconds. Toggle the time control when you need the countdown to a meeting or filing deadline, or leave it off for calendar-only timelines. The summary also surfaces zodiac signs, weekday of birth, and how far through the current birthday year you have travelled.
Visual progress cards show how much of the current year has passed and how many days remain until the next celebration. Supply an expected lifespan to see a second gauge that tracks how much of that plan you have already used, which helps when deciding on travel, fitness milestones, or retirement savings contributions. Copying the JSON payload preserves every component so you can archive snapshots in journals or dashboards.
Double check the timezone of any official record before entering the numbers because some registries store times in UTC while others use local offsets. Start by comparing the tool with the age printed on your identification, confirm it matches, and then adjust the target date for the scenario you are planning so downstream calculations stay credible.
Reach for this calculator when you want precision beyond quick estimates; use actuarial tables or medical guidance if you also need risk models, survival analysis, or clinical advice.
Birth and target instants are parsed as ISO-like strings and combined with optional clock times to obtain timezone-aware timestamps tb and tt. The primary difference Δs in seconds drives every downstream measurement, while the library also derives human readable components such as years, months, days, and remaining hours.
The tool computes integer year totals by subtracting birthdays until the target date is before the next anniversary, then calculates residual months and days relative to that anniversary. Fractional age in years uses floating-point math based on calendar-aware differences to avoid the rough approximation that simple 365-day divisions would produce.
Leap year handling for 29 February births is configurable: nearest uses 29 February on leap years and 1 March otherwise, feb28 maps to 28 February regardless of the year, and mar1 always selects 1 March. This choice affects both the next birthday calculation and the year-progress donut chart.
Optional lifespan estimates divide the decimal age by the provided lifespan in years to produce a percentage, while the countdown gauge computes days until the next birthday by subtracting the previous anniversary and taking the remaining span. Western and Chinese zodiac signs follow standard solar and twelve-year zodiac cycles respectively.
| Symbol | Meaning | Unit / datatype | Source |
|---|---|---|---|
| Birth instant constructed from date and optional time | UTC timestamp | Input | |
| Target instant for which age is calculated | UTC timestamp | Input | |
| Total elapsed seconds between instants | seconds | Derived | |
| Decimal age in years | years | Derived | |
| Progress through current birthday year | percent | Derived |
Set birth date to 1990-05-15 at 08:45, target date to 2024-10-19 at 12:30, keep leap handling on nearest, and request six decimal places for the fractional age.
The readable age is 34 years, 5 months, and 4 days, the decimal age is 34.432346 years, and 43.0 percent of the current birthday year has passed with 208 days remaining until the next celebration.
| Mode | Birthday mapping | When to use |
|---|---|---|
| Nearest | 29 Feb on leap years, else 1 Mar | Default compromise that keeps day counts consistent for most records. |
| Feb 28 | Always 28 Feb | Matches jurisdictions that celebrate leap birthdays on 28 Feb. |
| Mar 01 | Always 1 Mar | Use when payroll or policy pushes leap birthdays to March. |
Outputs follow the proleptic Gregorian calendar and the browser timezone; the tool does not apply historical calendar reforms.
Example: compare age on 2028-01-01 for a child born on 2012-02-29 using the Feb 28 mapping to align with school registration rules.
You will receive a complete age summary, countdown to the next birthday, zodiac context, and lifespan progress snapshot ready for planning documents.
| Parameter | Meaning | Unit / datatype | Typical range | Sensitivity |
|---|---|---|---|---|
| Date of birth | Calendar date the person was born | YYYY-MM-DD | 1900 to today | Baseline for all calculations |
| Birth time | Local time of birth if known | HH:MM | 00:00 to 23:59 | Improves sub-day precision |
| Target date | Date or timestamp for which to evaluate age | YYYY-MM-DD or ISO | >= birth date | Defines the reporting horizon |
| Leap mode | Rule for mapping leap birthdays on non-leap years | enum | nearest / feb28 / mar1 | Affects counts and warnings |
| Decimal digits | Precision for fractional year display | integer | 0 to 12 | Cosmetic; does not change raw math |
| Lifespan years | Self-imposed lifespan estimate | years | 0 to 120 | Enables lifespan progress badge |
Age totals use full double precision for internal arithmetic. Fractional years respect the requested decimal digits with a period as the separator. Percent values for year progress and lifespan progress are rounded to one decimal place, and countdown readouts display whole days while retaining fractional minutes in the JSON export.
| Field | Type | Accepted values | Notes | Placeholder |
|---|---|---|---|---|
| dateBirth | string | \d{4}-\d{2}-\d{2} | Invalid dates trigger a visible error message. | 1990-05-15 |
| includeTime | boolean | true / false | Gates whether times are considered. | false |
| birthTime | string | HH:MM | Defaults to 00:00 when includeTime is false. | 08:45 |
| dateTarget | string | \d{4}-\d{2}-\d{2} | Must be on or after the birth date. | 2024-10-19 |
| targetTime | string | HH:MM | Only parsed when includeTime is true. | 12:30 |
| leapMode | enum | nearest, feb28, mar1 | Controls 29 Feb birthdays on off-years. | nearest |
| decimalDigits | number | 0–12 | Values outside range clamp to safe bounds. | 6 |
| lifespanYears | number | ≥ 0 | Zero disables lifespan progress. | 90 |
| date_mode | enum | auto, tonight, tomorrow | Auto rolls past target to tomorrow if the time already passed. | auto |
| Channel | Content | Encoding | Precision |
|---|---|---|---|
| UI table | Age breakdown, zodiac, calendar facts | Locale text | Rounded per display settings |
| Year donut | Passed and remaining days in current year | ECharts series | One decimal percent |
| Countdown gauge | Hours and days until next birthday | ECharts gauge | Whole days on dial |
| JSON export | Inputs, totals, zodiacs, progress metrics | UTF-8 JSON | Full precision numbers |
| Query string | All parameters encoded for sharing | URL encoded | Exact |
No network calls are made; age calculations, charts, and exports run entirely in the browser based on the values you enter.
State resides in reactive memory and, after interaction, in the optional query string. Refreshing without the encoded parameters clears everything instantly.
Computations involve constant-time date differences and simple chart updates; complexity is O(1) with respect to the input size. Charts render only when their tabs are visible, and resize listeners are debounced to keep the page smooth on low-power devices.
Identical inputs produce identical age breakdowns, progress percentages, charts, and JSON exports. Leap mode decisions are deterministic and based solely on the selected policy and the target calendar year.
Inputs accept only structured date and time strings; numbers are range-checked before use. No external scripts process your data, clipboard operations use the platform API, and the app never injects user supplied HTML back into the page.
How exact is the age in years and days?
The tool uses calendar-aware differences, so values are exact down to the minute when you provide times; without times it assumes midnight local time for both endpoints.
Can I calculate age in a different timezone?
The calculator follows the timezone of your browser. To evaluate another timezone, temporarily change your system timezone or use the JSON output in a script that adjusts offsets.
Does the app store my birth date anywhere?
No. Everything runs locally, and nothing is sent to a server. Only your browser memory and optional share link ever contain the data.
How can I find how many seconds old I am?
Enable the time toggle, set the target date to now, and read the Seconds line in the metrics table or in the JSON export for the exact count.
Is there a cost or login requirement?
No. The calculator is free to use, requires no account, and you can copy or download results without limits.
Why does the next birthday sometimes jump a year ahead?
In auto mode, if the target time has already passed today, the next birthday rolls to the following year so countdowns never show negative values.
Date math follows the proleptic Gregorian calendar and ISO 8601 formatting. Average year length of 365.2425 days aligns with civil timekeeping standards, while zodiac designations follow conventional Western astrological date ranges and the 12-animal Chinese cycle.
Progress calculations mirror common age and milestone planning practices used in HR compliance checklists and educational enrollment guidelines.
All dates remain on your device unless you share the encoded link or exported files; clear the query string before distributing screenshots or demos that should not reveal personal information.