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2.6 Dates and time arithmetic

Checked against Microsoft's Excel for Windows keyboard references, August 2026

తెలుగులో చదవండి

What you'll be able to do

Do arithmetic on dates: days late, months of service, the end of a financial quarter. You will get the answer you expected, because you will know what Excel actually stores when it stores a date.

Before you start

A blank sheet is enough. Bring one real date question from your own life, such as a fee deadline or the length of a project, to answer at the end.

The work

  1. Same either way: see the machinery once, and the rest follows. Enter today's date with CtrlSemicolon. Then open Format Cells with Ctrl1 and set the cell's format to General. A plain number appears: the count of days since the start of 1900. A date is a number wearing date clothes. That is why subtracting, sorting and comparing all work. Set the format back the same way.
  2. Same either way: because dates are numbers, the days between two of them is a subtraction. =B2-A2 gives the days from A2 to B2. Days until a deadline is =B2-TODAY(), and =TODAY() stays current every time the file is opened.
  3. Same either way: two sets of functions build dates and take them apart. =DATE(2026, 8, 27) builds one safely from its parts, and no regional day-and-month confusion can touch that spelling. =YEAR(A2), =MONTH(A2) and =DAY(A2) take a date apart again.
  4. Same either way: months are uneven, so never add 30. =EDATE(A2, 3) lands exactly three calendar months later. =EOMONTH(A2, 0) is the last day of A2's own month, and =EOMONTH(A2, 2) is the month end two months on. That is how quarter ends and Indian financial-year boundaries, April to March, are worked out cleanly.
  5. Same either way: working days have their own arithmetic. =NETWORKDAYS(A2, B2) counts the weekdays between two dates, and it takes an optional range of holidays to skip. =WORKDAY(A2, 10) lands ten working days after A2, which is the honest version of "the deadline is in two weeks".
  6. Same either way: ageing bands put the pieces together. =IFS(TODAY()-A2<=30, "0-30", TODAY()-A2<=60, "31-60", TRUE, "60+") is the unpaid-bills report in one line. Every function in it comes from this lesson or the logic one.
  7. Same either way: the classic failure is text pretending to be a date. The tell is where it sits: a real date sits on the right of an unformatted cell, and text sits on the left. Text dates will not sort, subtract or band. Convert them with =DATEVALUE(A2) when the text is recognisable, or rebuild them with DATE and the text-cutting functions when the format is strange. Then paste values, as in the text lesson.

Try it

Work out your own date question. Then find the days until the next month end with =EOMONTH(TODAY(),0)-TODAY(). Then find the working days left this month, and an ageing band over three invented bill dates. Break a date on purpose by typing it inside quotation marks, and repair it with DATEVALUE.

Check yourself

A number: the days counted from the start of 1900. Numbers subtract, sort and compare, which is exactly what date arithmetic is.

Months run from 28 to 31 days, so adding 30 drifts. EDATE walks the calendar itself and lands on the same day of the next month.

NETWORKDAYS says how many working days lie between two dates. WORKDAY says which date falls a number of working days after a start. Both accept a list of holidays.

They are text. Check whether they sit on the left of their cells. Convert with DATEVALUE, or with DATE and the text functions, paste values, then sort.

Anchor it on March. For dates from April onward it is next year's 31 March, and =EOMONTH(DATE(YEAR(A2)+IF(MONTH(A2)>=4,1,0),3,1),0) builds it from parts you now own.

Go deeper

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Back to Dates and time arithmetic: work through the checklist