semkuDay of year calculator
Choose a date to find its day number, or enter a year and day number to find the date.
Day number rules
January 1 is day 1 of the year. To find a date from a day number, count from January 1 of the selected year.
Days remaining equal the total days in the year minus the day number. The selected date is excluded, so December 31 has 0 days remaining.
A year has 366 days if it is divisible by 4, except years divisible by 100 unless they are also divisible by 400. All other years have 365 days.
The same Gregorian calendar rules apply throughout years 0001–9999, including earlier dates, without converting historical calendar systems.
Today uses this device’s local calendar date and changes at local midnight.
The conversions cover calendar dates and day numbers within a year. For counting days between two dates, use the separate date calculator.
Day number = days in earlier months + day of month. Days remaining = total days in the year − day number. Leap year = divisible by 4 and either not divisible by 100 or divisible by 400. To reverse the calculation, count day number − 1 days after January 1.
Frequently asked questions
- Does the remaining-day count include the selected date?
- No. It counts only dates after the selected date through December 31. The remaining-day count on December 31 is 0.
- Why are day numbers from March onward one higher in a leap year?
- February has 29 days in a leap year instead of 28. That extra day adds 1 to the day number of each later date.
- Why can today’s day number differ on another device or website?
- This tool uses your device’s local date and changes at local midnight. A different time zone or device clock can give a different date. semku’s Days until calculator uses Korea Standard Time (KST).
- Does this convert other date-numbering systems?
- No. The day number starts at 1 each January and identifies a date within the selected year. The reverse conversion uses that same year and day number.
Privacy on this page
Calculations run in your browser. The date, year, day number and results are not sent to the server or kept in browser storage. The selected date is included after the # in the URL when you change it, so sharing that URL also shares the date. This part is not included in the page request sent to the server. The today line reads this device’s clock to determine its local date.
To understand how the page is used and to improve the service, this page sends semku’s own usage statistics and automatic error reports. They go only to the dedicated endpoint under semku.com/api/telemetry/v1/. They are not used for advertising or third-party tracking.
The usage statistics include stages of use (such as starting an operation or requesting a copy), the times they occur and fixed identifiers that distinguish the page and feature. They do not include the date, year or day number you enter, calculated dates, day numbers, days remaining, total days in the year, the local date used for today or copied text. Inputs are not sent as hashes or as size categories either. The full URL and search terms are not sent.
Operations and sessions are distinguished by randomly generated identifiers. In the browser, these identifiers exist only in temporary memory and are not written to cookies or browser storage. No identification based on cookies or combined device characteristics is used.
Error reports contain the error type, code and time, and, where available, a registered program-source identifier with line and column numbers. The error message text and stack traces are not sent. Usage statistics and error reports also carry the site identifier, the deployment version and a random record identifier. For access records such as IP addresses, browser signals (User-Agent Client Hints), region and language, see the paragraph below.
The feedback form sends the rating you chose and the text you typed in the free-text field when you press the send button. The form also sends a random ID that distinguishes the submission, along with the page, site, deployment version and type of request. There are no fields for your name, email address or phone number, and the date, year or day number you enter, calculated dates, day numbers, days remaining, total days in the year, the local date used for today or copied text are not attached automatically. Before sending your text, the widget removes leading and trailing whitespace and, if you selected a rating, adds [+1] or [-1] at the start; it makes no other changes to your text. After receipt, the collector standardizes line endings and removes leading and trailing whitespace. Please do not enter personal data, passwords, authentication keys or payment details.
To improve the service, we record the country and state/province-level region at the time of your visit (an estimate based on the connecting network), which site you came from including the page path, and one display-language setting announced by your browser (for example, en-US). Location is kept to country and region only; no city or precise position is recorded. When you use the service, connection records, including your IP address, are automatically generated and retained to maintain service security and identify abnormal access. Cloudflare is the data processor for this site. Collection of this item is enabled only after this notice is published; we do not collect it retrospectively for use before collection is enabled. Query strings such as search terms are not recorded, and neither is the full list of preferred languages or the raw request headers. Collection of this information is currently disabled and will only be enabled after this notice is published. If we enable collection, we will collect and use signals your browser reports about its type and version, along with an indication of whether automation tools are being used, to identify bots. These browser signals are estimates and do not conclusively identify your browser's type or version or whether automation tools are being used. We do not collect it retrospectively for use before collection is enabled. The raw User-Agent request header is not recorded. These records are per visit only and use no identifier that links one visit to another. Recording starts only with visits after this notice is published and is not applied retroactively to earlier visits. The region and the referring site have been recorded since 2026-09-20; the display language since 2026-09-24. Browser signals are not recorded yet.
Separately, when you visit the site, the hosting provider records your IP address, the time of the request and user-agent information about your browser and device in Cloudflare Pages’ standard access logs.
For details, see the privacy policy.
Calculations run in your browser without sending your calculation inputs or results to the server.