Age in years, months and days calculator
Get an exact age in whole years, months and days between a birth date and a day you choose: someone born on 15 May 1990 is 36 years, 2 months and 10 days old on 25 July 2026. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Birth date
- 1990-05-15
- Reference date
- 2026-07-25
- Years
- 36
- Months
- 2
- Days
- 10
- Total days
- 13,220
People searching for an age in years months days calculator want a civil breakdown that forms, HR systems, and parents can trust: not a rough year total and not a floating average of thirty point four days. This tool takes a birth date and a required reference date, never invents today from the server clock, and returns whole years, remaining months, and leftover days under proleptic Gregorian rules with end-of-month clamping.
How years, months, and days are counted on the civil calendar
The algorithm measures whole calendar months from the birth date toward the reference date, clamping the day-of-month when the target month is shorter—so a birth on the thirty-first of January advances one month to the last day of February in leap and non-leap years alike. If that provisional month-advanced date would overshoot the reference, the engine steps back one month and reports the remaining span as whole days between the adjusted intermediate date and the reference.
Years are simply the whole-month total divided by twelve; months are the remainder modulo twelve; days complete the triple. Edge cases such as a leap-day birth measured on February twenty-eight in a non-leap year follow the same clamp rule used when adding months, so the anniversary logic stays consistent with the rest of the KIT calendar family.
What you can do with it
Eligibility and age-gate forms
Pass a fixed birth date and a cut-off reference date to show years, months, and days for school enrollment, contest age groups, or regulated product access without host clock drift.
Pediatric and parenting charts
Compute exact age in years, months, and days for well-child visits and milestone trackers using the visit date as the explicit reference.
FAQ
What if the reference date is before the birth date?
Age cannot be negative; fix the pair or swap fields only if your product intentionally measures a future birth.
How are end-of-month and leap-day birthdays handled?
Months advance with clamp to the last valid day of the target month. Remaining days are whole civil days after that advance, matching common calendar anniversary rules.
What does the age in years months days calculator cost?
The browser tool is free on your device.
Does it use today's date automatically?
No. You always choose the reference day yourself, and the calculator never reads a clock. That way the same two dates give the same age on any device, which matters for forms and audits.
Can I enter a date that includes a time?
Yes, but only the calendar date is used. An age in years, months and days is measured from one date to another, so the time of day and the time zone do not change the result.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/date/age-months-days \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"birth_date":"1990-05-15","reference_date":"2026-07-25"}'const res = await fetch("https://api.kit.forhosting.com/date/age-months-days", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"birth_date": "1990-05-15",
"reference_date": "2026-07-25"
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/date/age-months-days",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"birth_date": "1990-05-15",
"reference_date": "2026-07-25"
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/date/age-months-days", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"birth_date":"1990-05-15","reference_date":"2026-07-25"}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"birth_date":"1990-05-15","reference_date":"2026-07-25"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/date/age-months-days", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"birth_date": "1990-05-15",
"reference_date": "2026-07-25"
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "date.age_months_days",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
Invalid calendar days fail with invalid_input and are not billed; successful items cost $0.002 from KIT balance.
Birth date, reference date, and why the clock is never used
Each value should be a civil calendar day in YYYY-MM-DD form, for example nineteen ninety hyphen zero five hyphen fifteen for a birth date and two thousand twenty-six hyphen zero seven hyphen twenty-five for the snapshot day. You may prefix a full ISO-8601 datetime; if a time is present only the calendar date part is used, because civil age is a date-to-date measure, not a clock duration with time zones. Years range from one through nine thousand nine hundred ninety-nine, months must be one through twelve, and the day must exist in that month under Gregorian leap rules, including February twenty-nine only in leap years. Send two required string fields: birth_date and reference_date. Optional aliases birth, birthdate, dob, and from map to the birth field; reference, as_of, to, and on map to the reference field so form builders and SDKs can keep familiar names. Both endpoints are mandatory on purpose: an age calculator that silently substitutes the host wall clock produces different answers in CI, on a phone flying across the Pacific, and on a server in UTC, which breaks eligibility audits and reproducible exports. Impossible pairs such as two thousand twenty-three hyphen zero two hyphen twenty-nine are rejected with invalid_input instead of being clamped into March. If the reference date falls strictly before the birth date, the request fails with a clear message that age cannot be negative, rather than inventing a signed age that most product UIs would mislabel as how old someone is.
How years, months, and days are counted on the civil calendar
On success the response echoes normalized birth_date and reference_date as YYYY-MM-DD, then years, months, and days as non-negative integers that together describe exact civil age. Field total_days is the exclusive civil day difference between the two ordinals: the same calendar day yields zero total days and zero years, months, and days, while the next calendar day yields one day of age.
API usage, pricing, product workflows, and honest limits
Use the free in-browser age in years months days calculator for parent dashboards, classroom demos, and one-off eligibility checks without installing moment libraries or shipping a timezone database to every client. Keep expectations honest: this capability measures Gregorian civil age between two explicit dates; it does not skip weekends as business age, load public holiday calendars, convert lunar ages, or default the reference to today on the server. Source inputs follow the same retention rules as other KIT parse items. POST a compact JSON body with birth_date and reference_date strings. Call the prepaid API when HR onboarding, pediatric charts, sports age groups, visa forms, or insurance underwriting need a stable contract under KIT balance at $0.002 per successful item; validation failures never consume balance after the engine rejects the request. Pair this endpoint with a pure day-count tool when you also need an unordered span length alone, or with month-between helpers when the product copy talks only in whole months for infants. SDK authors can map years, months, and days into three numeric widgets and surface the formatted string for accessibility labels, using the same response shape in every language binding.
Integration use cases
HR tenure and anniversary snapshots
Store civil age or service age against a payroll or audit date so exports and golden tests reproduce the same triple every time.
Technical questions
How do I calculate age in years, months, and days?
Send JSON with birth_date and reference_date as YYYY-MM-DD. The response includes years, months, days, total_days, and a formatted string such as "36 years, 2 months, 10 days".
Does this use today's date automatically?
No. reference_date is required. The engine never reads the system clock, so results stay identical in CI, browsers, and API workers.