Inputs
IANA name, e.g., Asia/Karachi, America/New_York.
Choose December 1, December 31, or set a specific day.
Result
Exports the rows in the table below.
Example Data & Your Scenarios
| # | As-of (ISO) | Zone | Target | Rounding | Inclusive | Days Until | Note | Actions |
|---|
Edit cells inline except the calculated value; recalc by clicking the row's refresh.
Formula Used
Let t₀ = as-of date-time in selected time zone. Let D = target date in December at 00:00 in same zone. Compute Δ = D − t₀ in milliseconds. days_exact = Δ / 86,400,000 If rounding = "ceil": days = ceil(days_exact) If rounding = "floor": days = floor(days_exact) If rounding = "exact": days = days_exact (to 6 decimals) If "Include start date" is checked, add 1 to the integer result. If t₀ is after D, move D to December of the next calendar year.
How to Use This Calculator
- Leave “Use current date and time” on for a live countdown.
- Set an explicit date/time to plan for a different day.
- Choose December 1, December 31, or a specific December day.
- Pick rounding; “ceil” is typical for countdowns shown to users.
- Toggle “Include start date” if you count today as day one.
- Click Calculate to see the summary and details.
- Use Add to table to log scenarios for export.
- Export your table as CSV or a quick PDF report.
Days Until December: Weeks and Hours View
Translate the day count into weeks, days, and hours for quick briefings. Use weeks = floor(days) ÷ 7 and remaining = floor(days) mod 7. For fine detail, compute hours ≈ days_exact × 24 and minutes ≈ days_exact × 1440.
Business Days Until December
When planning work, exclude weekends and local holidays. A quick approximation is business_days ≈ total_days − 2 × full_weeks − weekend_overhang. Exact values require a holiday calendar for the selected region and time zone.
Edge Cases and Countdown Rules
- If today is after the chosen December date, the target rolls forward to next year.
- Inclusive counting adds one when showing integer days (not used for exact).
- Rounding choice affects display only; underlying exact milliseconds stay unchanged.
- DST changes and time-zone offsets are handled using Luxon’s zone-aware arithmetic.