Day Calculator
Instantly check the day of week and key calendar stats for any date
Table of Contents
How to Use
- Pick any date using the calendar input or type it manually in YYYY-MM-DD format.
- Select “Calculate Day Info” to run the calendar analysis.
- Review the highlighted day of the week along with week number, quarter, and day-of-year details.
- Use the weekend and leap-year badges to plan schedules, events, and reminders.
What the Day Calculator Reveals
Every date carries multiple calendar insights beyond the day of the week. Our calculator evaluates the modern Gregorian calendar to tell you exactly where a date falls in the year, which helps with planning, reporting, and historical lookups.
- Pinpoint the weekday name (Monday through Sunday) for any past or future date
- Track the ISO week number that businesses and academic institutions use for scheduling
- Confirm whether a date is part of a leap year and how many days exist in that year
- View the exact quarter and day-of-year position to support fiscal and seasonal planning
Understanding the Calendar Metrics
The results panel displays multiple data points that make calendar math faster. Each metric is calculated directly from the selected date without needing manual formulas.
- Day number: Zero-based index where Sunday is 0 and Saturday is 6, matching JavaScript’s native getDay() method.
- Week number: Uses the ISO 8601 standard. Week 1 is the week that contains the first Thursday of the year.
- Quarter: Divides the year into four equal fiscal segments (Q1–Q4).
- Day of year: Counts days from January 1. Leap years include a 366th day on February 29.
- Days in month/year: Quickly review how many days remain in the current month or year for project timelines.
Weekend and Leap Year Checks
Weekend status helps teams schedule deadlines, shipping dates, and on-call rotations. Leap year checks are essential when working with recurring billing cycles, payroll periods, or legal deadlines that depend on precise day counts.
- Weekend detection flags Saturdays and Sundays instantly for quick go/no-go decisions.
- Leap year verification follows the Gregorian rule: divisible by 4, except centuries not divisible by 400.
- Days-in-month data factors in 28/29 days for February automatically.
Practical Uses for Day Insights
- Plan marketing launches or newsletters to avoid weekends and holidays
- Align fiscal or academic week numbers with project management tools
- Validate due dates and compliance deadlines that fall near month-ends
- Prepare event timelines, travel itineraries, or countdowns to special dates
- Verify historical dates when researching family records or anniversaries
Frequently Asked Questions
- Which calendar system does this tool use?
- The day calculator uses the proleptic Gregorian calendar, the same system used across most of the world today. That means it works reliably for modern and future dates as well as historical dates after 1582.
- How is the ISO week number determined?
- Week numbers follow ISO 8601 rules. Week 1 is the first week that contains at least four days in the new year, and weeks always start on Monday. This standard keeps schedules consistent across international businesses.
- Why is the day number zero-based?
- JavaScript’s native Date object returns Sunday as 0 through Saturday as 6. We expose that same convention so developers can copy results directly into scripts or spreadsheets without extra conversion.
- Can I use the calculator for long-term planning?
- Yes. The tool works for any valid Gregorian date, so you can check far future deadlines, recurring events, or historical anniversaries instantly.