Converting Excel Date Serial Number to Date using

Question

I have the following javascript code that convert date (string) to the Date Serial Number used in Microsoft Excel:

function JSDateToExcelDate(inDate) {

    var returnDateTime = 25569.0 + ((inDate.getTime() - (inDate.getTimezoneOffset() * 60 * 1000)) / (1000 * 60 * 60 * 24));
    return returnDateTime.toString().substr(0,5);

}

So, how do I do the reverse? (Meaning that a Javascript code that convert the Date Serial Number used in Microsoft Excel to a date string?

Answer 1

// Parses an Excel Date ("serial") into a
// corresponding javascript Date in UTC+0 timezone.
//
// Doesn't account for leap seconds.
// Therefore is not 100% correct.
// But will do, I guess, since we're
// not doing rocket science here.
//
// https://www.pcworld.com/article/3063622/software/mastering-excel-date-time-serial-numbers-networkdays-datevalue-and-more.html
// "If you need to calculate dates in your spreadsheets,
//  Excel uses its own unique system, which it calls Serial Numbers".
//
lib.parseExcelDate = function (excelSerialDate) {
  // "Excel serial date" is just
  // the count of days since `01/01/1900`
  // (seems that it may be even fractional).
  //
  // The count of days elapsed
  // since `01/01/1900` (Excel epoch)
  // till `01/01/1970` (Unix epoch).
  // Accounts for leap years
  // (19 of them, yielding 19 extra days).
  const daysBeforeUnixEpoch = 70 * 365 + 19;

  // An hour, approximately, because a minute
  // may be longer than 60 seconds, see "leap seconds".
  const hour = 60 * 60 * 1000;

  // "In the 1900 system, the serial number 1 represents January 1, 1900, 12:00:00 a.m.
  //  while the number 0 represents the fictitious date January 0, 1900".
  // These extra 12 hours are a hack to make things
  // a little bit less weird when rendering parsed dates.
  // E.g. if a date `Jan 1st, 2017` gets parsed as
  // `Jan 1st, 2017, 00:00 UTC` then when displayed in the US
  // it would show up as `Dec 31st, 2016, 19:00 UTC-05` (Austin, Texas).
  // That would be weird for a website user.
  // Therefore this extra 12-hour padding is added
  // to compensate for the most weird cases like this
  // (doesn't solve all of them, but most of them).
  // And if you ask what about -12/+12 border then
  // the answer is people there are already accustomed
  // to the weird time behaviour when their neighbours
  // may have completely different date than they do.
  //
  // `Math.round()` rounds all time fractions
  // smaller than a millisecond (e.g. nanoseconds)
  // but it's unlikely that an Excel serial date
  // is gonna contain even seconds.
  //
  return new Date(Math.round((excelSerialDate - daysBeforeUnixEpoch) * 24 * hour) + 12 * hour);
};

Answer 2

So, there I was, having the same problem, then some solutions bumped up but started to have troubles with the Locale, Time Zones, etc, but in the end was able to add the precision needed

toDate(serialDate, time = false) {
    let locale = navigator.language;
    let offset = new Date(0).getTimezoneOffset();
    let date = new Date(0, 0, serialDate, 0, -offset, 0);
    if (time) {
        return serialDate.toLocaleTimeString(locale)
    }
    return serialDate.toLocaleDateString(locale)
}

The function's 'time' argument chooses between displaying the entire date or just the date's time

Answer 3

It's an old thread but hopefully I can save you the time I used readying around to write this npm package:

$ npm install js-excel-date-convert

Package Usage:

const toExcelDate = require('js-excel-date-convert').toExcelDate;
const fromExcelDate = require('js-excel-date-convert').fromExcelDate;
const jul = new Date('jul 5 1998');

toExcelDate(jul);  // 35981 (1900 date system)

fromExcelDate(35981); // "Sun, 05 Jul 1998 00:00:00 GMT"

You can verify these results with the example at https://docs.microsoft.com/en-us/office/troubleshoot/excel/1900-and-1904-date-system

The Code:

function fromExcelDate (excelDate, date1904) {
  const daysIn4Years = 1461;
  const daysIn70years = Math.round(25567.5 + 1); // +1 because of the leap-year bug
  const daysFrom1900 = excelDate + (date1904 ? daysIn4Years + 1 : 0);
  const daysFrom1970 = daysFrom1900 - daysIn70years;
  const secondsFrom1970 = daysFrom1970 * (3600 * 24);
  const utc = new Date(secondsFrom1970 * 1000);
  return !isNaN(utc) ? utc : null;
}

function toExcelDate (date, date1904) {
  if (isNaN(date)) return null;
  const daysIn4Years = 1461;
  const daysIn70years = Math.round(25567.5 + 1); // +1 because of the leap-year bug
  const daysFrom1970 = date.getTime() / 1000 / 3600 / 24;
  const daysFrom1900 = daysFrom1970 + daysIn70years;
  const daysFrom1904Jan2nd = daysFrom1900 - daysIn4Years - 1;
  return Math.round(date1904 ? daysFrom1904Jan2nd : daysFrom1900);
}

If you want to know how this works check: https://bettersolutions.com/excel/dates-times/1904-date-system.htm

Answer 4

No need to do any math to get it down to one line.

// serialDate is whole number of days since Dec 30, 1899
// offsetUTC is -(24 - your timezone offset)
function SerialDateToJSDate(serialDate, offsetUTC) {
  return new Date(Date.UTC(0, 0, serialDate, offsetUTC));
}

I'm in PST which is UTC-0700 so I used offsetUTC = -17 to get 00:00 as the time (24 - 7 = 17).

This is also useful if you are reading dates out of Google Sheets in serial format. The documentation suggests that the serial can have a decimal to express part of a day:

Instructs date, time, datetime, and duration fields to be output as doubles in "serial number" format, as popularized by Lotus 1-2-3. The whole number portion of the value (left of the decimal) counts the days since December 30th 1899. The fractional portion (right of the decimal) counts the time as a fraction of the day. For example, January 1st 1900 at noon would be 2.5, 2 because it's 2 days after December 30st 1899, and .5 because noon is half a day. February 1st 1900 at 3pm would be 33.625. This correctly treats the year 1900 as not a leap year.

So, if you want to support a serial number with a decimal, you'd need to separate it out.

function SerialDateToJSDate(serialDate) {
  var days = Math.floor(serialDate);
  var hours = Math.floor((serialDate % 1) * 24);
  var minutes = Math.floor((((serialDate % 1) * 24) - hours) * 60)
  return new Date(Date.UTC(0, 0, serialDate, hours-17, minutes));
}

Answer 5

Although I stumbled onto this discussion years after it began, I may have a simpler solution to the original question -- fwiw, here is the way I ended up doing the conversion from Excel "days since 1899-12-30" to the JS Date I needed:

var exdate = 33970; // represents Jan 1, 1993
var e0date = new Date(0); // epoch "zero" date
var offset = e0date.getTimezoneOffset(); // tz offset in min

// calculate Excel xxx days later, with local tz offset
var jsdate = new Date(0, 0, exdate-1, 0, -offset, 0);

jsdate.toJSON() => '1993-01-01T00:00:00.000Z'

Essentially, it just builds a new Date object that is calculated by adding the # of Excel days (1-based), and then adjusting the minutes by the negative local timezone offset.

Answer 6

Try this:

function ExcelDateToJSDate(serial) {
   var utc_days  = Math.floor(serial - 25569);
   var utc_value = utc_days * 86400;                                        
   var date_info = new Date(utc_value * 1000);

   var fractional_day = serial - Math.floor(serial) + 0.0000001;

   var total_seconds = Math.floor(86400 * fractional_day);

   var seconds = total_seconds % 60;

   total_seconds -= seconds;

   var hours = Math.floor(total_seconds / (60 * 60));
   var minutes = Math.floor(total_seconds / 60) % 60;

   return new Date(date_info.getFullYear(), date_info.getMonth(), date_info.getDate(), hours, minutes, seconds);
}

Custom made for you :)