b2KIT

Birthday Reminder List

Store birthdays with names and dates, sorted by upcoming, with age calculation and countdown display.

Tested tool guide Tested browser tools Checked August 16, 2026

What Birthday Reminder List does, with a checked example

This tool stores a list of birthdays, each with a name and date, and presents them in order of the next upcoming birthday. For each entry it shows the number of days until that birthday and the age the person will turn on that date. Unlike a simple calendar, it rolls the date forward each year, so a birthday that already passed this year appears with its countdown to next year. The most common surprise is that the age shown is the age at the next birthday, not the current age today.

Worked example

A concrete input and expected output from the current implementation.

Input

Name: Alice
Date: 2000-03-11
Name: Bob
Date: 1995-09-22
Name: Carol
Date: 1988-01-30

Expected output

Alice - birthday Mar 11 - 63 days until next birthday - will turn 25
Bob - birthday Sep 22 - 258 days until next birthday - will turn 30
Carol - birthday Jan 30 - 23 days until next birthday - will turn 37

Assuming today is 2025-01-07, the next birthdays in chronological order are Carol (Jan 30), Alice (Mar 11), and Bob (Sep 22). Ages are computed at the upcoming birthday.

How the result is produced

1

Date entry

You enter a name and a date in a standard format such as YYYY-MM-DD. The tool parses the date and stores the birth year and month/day separately so it can compute the next occurrence each year. It treats the date as local time, not UTC, to avoid off-by-one errors in the countdown.

2

Sorting and display

For each entry, the tool finds the next birthday after today's date, then sorts the list by that upcoming date ascending. For each, it calculates the number of days until that date and the age that will be reached on that birthday. The display shows the name, the upcoming date, a countdown in days, and the age at that birthday.

Good uses

  • Planning a surprise party: check who has a birthday within the next week and how old they'll be.
  • Setting up recurring reminders: note the countdown to each upcoming birthday so you can schedule a card or call.
  • Quickly answering 'when is my colleague's birthday this year?' without checking a calendar app.

Limits and checks

  • The age shown is the age at the next birthday, not the current age. If someone's birthday hasn't occurred yet this year, the age is one more than their current age.
  • If you enter a date that is today, the countdown is 0 days and the age is the birthday age reached today. The tool treats 'today' as the day you view it, so results change daily.
  • Leap day birthdays (Feb 29) are handled the way the date library treats them, which may mean the birthday is observed on Feb 28 or Mar 1 in non-leap years. This might differ from your personal convention.

Common questions

What date format should I use when entering a birthday?

Use the YYYY-MM-DD format, for example 2000-03-11. Other common formats may be accepted, but YYYY-MM-DD is unambiguous and avoids confusion between month and day order.

Does the tool account for time zones when calculating the countdown?

Countdowns are based on your browser's local time zone. If you travel to a different time zone, the displayed countdown may shift by a day depending on the time of day. There is no per-entry time zone setting; it always uses the time zone of the device viewing it.

References and verification

The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.

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