Date and Time Calculators
Day of the Week Calculator
Day of the Week Calculator find a date's weekday, ordinal day, ISO week date, quarter, and leap-year status.
Date and Time Calculators
Day of the Week Calculator
Find a date's weekday, ordinal day, ISO week date, quarter, and leap-year status.
Formula
Weekday uses the proleptic Gregorian calendar. ISO week numbering assigns weeks to Thursday and defines week 1 as the week containing January 4.
About the Day of the Week Calculator
Find a date's weekday, ordinal day, ISO week date, quarter, and leap-year status. Date and time calculators apply calendar-aware or duration-aware arithmetic to the dates, times, zones, and intervals requested by the form.
How the Day of the Week Calculator Works
Weekday uses the proleptic Gregorian calendar. ISO week numbering assigns weeks to Thursday and defines week 1 as the week containing January 4.
The calculation runs in your browser. Submitted values are validated for the required numeric range, data shape, units, and method-specific restrictions before a result is shown.
Required Inputs
- Calendar date (required)
Results Reported
The result panel shows the final answer together with the intermediate quantities needed to audit the calculation. Depending on this method, reported values include:
dateweekdayweekday_number_isoday_of_yeariso_weekiso_week_yearquarterleap_yeardays_in_year
Day of the Week Calculator Example
Use the example data button, calculate, then review the result table, formula, and worked solution before using the answer.
| Input | Example value |
|---|---|
| Calendar date | 2026-07-11 |
How to Use the Calculator
- Confirm that the calculator title and method match the quantity, test, conversion, or planning question you need to solve.
- Enter values with compatible units and the requested sample, group, matrix, count, date, or option format.
- Select Example Data to inspect a valid input layout, or enter your own values and select Calculate.
- Review the result table, formula, worked substitutions, warnings, and interpretation rather than using only the headline number.
- Use Copy Result or Download CSV when you need a reusable record of the displayed calculation.
Understanding the Result
Calendar months, leap days, end-of-month rules, overnight intervals, and time zones are handled differently from fixed-length elapsed seconds.
Keep the entered values, units, selected options, and any warning shown beside the result. For a hypothesis test, report the statistic, degrees of freedom where applicable, p-value, alpha level, effect size, and decision. For an estimate or conversion, report the formula convention and final unit.
Accuracy and Limitations
The calculator keeps full browser precision during calculation and rounds only for display. Accuracy still depends on correct inputs and on whether the displayed model represents the real problem. Educational calculators cannot replace required professional review, current official rules, field measurements, laboratory methods, or specialist statistical software where those are necessary.
Frequently Asked Questions
What does the Day of the Week Calculator calculate?
Find a date's weekday, ordinal day, ISO week date, quarter, and leap-year status.
Which formula does the Day of the Week Calculator use?
Weekday uses the proleptic Gregorian calendar. ISO week numbering assigns weeks to Thursday and defines week 1 as the week containing January 4.
Is this a separate calculator?
Yes. This page has its own public URL, inputs, formula notes, browser function, fixture, and worked solution.
What should I verify before using the answer?
Check the entered values, units, selected options, formula convention, warnings, and result interpretation shown on this calculator page.