Half Birthday Calculator

Enter your birth date to instantly find the next half-birthday and how many days remain. Works across months and leap years, with a shareable result link.

Find Your Next Half-Birthday

Your Results

Dec 15, 2025(UTC)

Days until: 69

Previous Half-Birthday

Jun 15, 2025

Days since previous

114

Display timezone

Calculated in UTC to avoid timezone shifts. Switch to Local if needed.

Repeat yearly

Overview & Quick Facts

What it shows

• Next half-birthday date
• Days remaining from today
• Shareable result link

Good to know

• Handles leap years
• End-of-month birthdays supported
• Based on UTC date math

How to Calculate

Half-Birthday Formula

Rule: Next half-birthday is the earliest date ≥ today in the sequence DOB + k × 6 months (k ∈ ℕ).

Note: If the target month has fewer days, use its last valid day.

Steps

1
Enter your date of birth
Use the YYYY-MM-DD format for consistency
2
Generate 6‑month increments
Start from DOB, then add six months repeatedly
3
Pick the first date ≥ today
Compute days remaining from today

Important Considerations

⚠️ Notes

Dates are computed in UTC and clamped to valid calendar days.

End-of-month birthdays

If a month has fewer days, we use its last valid day.

• Example: Jan 31 → Jul 31
• Mar 31 → Sep 30

Leap year handling

Feb 29 births increment by six months safely.

• Feb 29 → Aug 29
• Uses calendar-safe month math

Time zones

We standardize to UTC to avoid boundary shifts.

• Day-level accuracy
• Local time may display differently

Sharing

Shared links only include your DOB (optional reference date).

• No personal identifiers
• Easy to reproduce results

Example Cases

Case 1: DOB = 1995-06-15

Input: 1995-06-15

Next Half-Birthday: Dec 15, 2025
Days Until: Varies by today

Six months after June 15 is December 15 each cycle.

Case 2: DOB = 2000-01-31

Input: 2000-01-31

Next Half-Birthday: Jul 31 (or last day of month when needed)

End-of-month handling preserves the last valid calendar day.

Tips & Notes

Planning reminders

• Set a calendar alert a week before
• Consider time zones for friends abroad
• Share the link so others can prefill

Common formats

• YYYY-MM-DD is preferred
• Mobile date pickers are supported
• UTC ensures day-level accuracy

Occasions & Ideas

Low-key celebrations

• Coffee or dessert treat
• Book a movie night
• Send a small card

Family & kids

• Half-cake theme
• Small gift or activity
• Photo memory each cycle

Frequently Asked Questions

What is a half-birthday?

A half-birthday is the date exactly six months after your birthday. This tool finds the next upcoming half-birthday from today.

How is the next half-birthday calculated?

We add six-month steps from your birth date until we reach a date on or after today. End-of-month birthdays are handled by rolling to the last valid day of the target month.

Does the calculator handle leap years and Feb 29 birthdays?

Yes. Dates are computed in UTC and month overflow is clamped to the last valid day. Feb 29 will map to Aug 29 in non-leap sequences, based on six-month increments.

What does "days until" mean?

It is the number of full days between today and your next half-birthday. If it is today, the value shows 0.

Can I share my result with others?

Yes. Use the Share button to copy a link that pre-fills your birth date so others can see the same result.