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Prevent Duplicate Data Entry using Cell Validations



We all know that data validation is a very useful feature in Excel. You can use data validation to create a drop-down list in a cell and limit the values user can enter. But, do you know that you can use data validation in a multitude of ways to prevent users from entering wrong data?

Here is a practical application: Prevent users from entering duplicate values in a range of cells.

For eg. you are making an invoice. Wouldn’t it be cool if Excel prompted you when you enter a duplicate line item so that increase the item quantity instead of repeating it.

Here is a 3 step tutorial to do just that.

Step 1: Identify the range of cells where you want only unique values to be entered

This is simple. All you have to do is find the range where you want to control the user input. Lets say the range is B4:B11

Step 2: Set up Data Validation to prevent duplicate entries

Select the range (B4:B11) and go to data validation (Excel 2007: Data Ribbon > Data Validation, or press ALT+AVV)

Using Data Validation to prevent DuplicatesNow, specify the validation type as “Custom”, this will allow us to use formulas to check for valid data. In our case, we need check if a particular entry is duplicated in the range B4:B11. This can be easily done using COUNTIF formula [learn COUNTIF Formula in plain English].

Go to the formula field and type the countif formula like this: =COUNTIF($B$4:$B$11,B4)<=1

Also, you can set up the “Error Alert” so that you can show a custom message when a duplicate value is typed, like “You have already added that product” message.

Data Validation - Error message

Once you set up error message, it will show up like this:

Data validation to prevent duplicates - error message example
Step 3: Sit back and Relax

The third step is all too familiar. Now that you have prevented duplicate entries in your spreadsheets you can sit back and relax. May be read a few more spreadcheats.

More kickass stuff on data validation (and working with duplicates) using excel

There are a ton of useful articles on the site related to data validation and working with duplicates using excel. Here is a sample. Get started and learn something useful today.

This post is part of our spreadcheats series (yes, the series is still going after one year 😛 )


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42 Responses to “Prevent Duplicate Data Entry using Cell Validations”

  1. Jair says:

    Hi Chandoo, I need you help in the following problem.
    I'm trying to get a direccion from a found result. With this dirreccion I will want the before cell value. For example, If result of a find is 38 localized in cell $C$2, I need to get previus value (cell $B$2 ), maybe Andrés.

    Do you know some way to do that?

    Thank you for you help.

  2. Lincoln says:

    Hi Chandoo

    Thanks for this. One thing though: In my pre-2007 version of Excel, the COUNTIF function doesn't recognise a semicolon (;), but requires a comma.

    Is the semicolon an Excel 2007 thing?

  3. Chandoo says:

    Jair... I am not sure I understand what you want. what do you mean by Dirreccion?

    @Lincoln: I am sorry, often I forget that I am using European version of excel where the delimiter is ; instead of ,. I have corrected the formula now.

  4. subbu says:

    Thanks for this nice tip, i used to do a find all after filling every new items which was cumbersome.

    Do you know a way to extend this validation search to other tabs/sheets ?

  5. Jair says:

    Thanks for you attention. I'm trying to get of value continue from a found value. Let me show a example:

    Name Years
    John 35
    Maria 28
    Teresa 32

    If I search the max years, the result is 35, but I need that result to be John. Do you know how I can do it?

  6. Chandoo says:

    @Subbu.. you can easily extend the validation to other sheets by pasting the data validations. See the latest article here: http://chandoo.org/wp/2009/10/28/copy-data-validations/

    @Jair.. you can use the large() or small() formulas to do this. for eg. =index(A1:A3,large(B1:B3,1)) will get you the name of the person with highest "years". More help here: http://chandoo.org/excel-formulas/large.html

  7. Jair says:

    Hi, I don't know if I'm using bad the formula or its performance is diferent for my Office version. Large() formula return the value in the cell, in my example 35. The index() formula use a range, row and column. I'm using the large() as number of row, and it is bad because into the range don't have row 35. This is my perception. What do you think?

  8. Chad says:

    I am trying to attempt data validation in Excel Mobile, but the DV tool isnt available. I want to prevent duplicates is all, any advice on acheiving this in Excel Mobile? Thanks..

  9. Chandoo says:

    @Jair... my french aint that good. it starts at "merci" and ends at "beau coup".

    Anyhow, you need to merge the large with vlookup to do this. I am not sure if you have solved the problem. Otherwise let me know with details and I can write the formula in comments.

    @Chad... I have never used excel mobile, so I have no idea. May be they have not implemented data validations in excel mobile.

    Any excel mobile users out there?

  10. Jair says:

    Hi Chandoo, the proposed solution by JlD is interesting. He created a macro to get values when the matrix is not one dimensional, how on my problem. This fuction for me.
    I would like to share you my work, how can I upload?

  11. Chandoo says:

    @Jair.. sorry for such a delayed reply.. you can upload the files to skydrive and link them here. Or you can email them to me at chandoo.d @ gmail.com and I will upload them somewhere. But it could take forever if you email files to me as I am a bit lazy.

  12. [...] Day 31: Advanced Data Validation Tricks in Excel – Part 2 [...]

  13. Muhammad Moin says:


    Can you help me in Microstrategy?


  14. Ramprasad says:

    really wonderful article. I feel it is implementing Primary Key concept into spreadsheets.

  15. sriram says:

    Hi article on data validation. Excel is a very versatile platform to work with and we use it for all kinds of data tabulation. In fact this must have been the most rudimentary data management tools I must have worked with and knowing such tips only adds functuionality to our user experience. Great article. looking forawrd to read more.

  16. Vasanth says:

    Hi Chandoo,

    Thanks for such a nice idea.

    I tried copy paste the data into the validated area, but the pop-up msg (warning msg) doesn't came. Is it something that we need to update the data manually each time,.

    Do we have any option where we can bulk upload the number and it throws a warning message that the data already exits and do we want to continue with this ?

    Please do reply me.

    Thank you.


  17. kochu says:

    It was really useful chandoo...thanks a lot...

  18. Leo says:

    Tried this in excel 2010 and it did not work?
    Could the newer excel have changed that much?

    • Hui... says:


      It works fine in Excel 2010

      The formula used above =COUNTIF($B$4:$B$11,B4)<=1

      only applies to the range B4:B11

      Did you adjust the range to your data?

  19. Tariq Khan says:

    This page helped me accurately to find solution of my question. thanx

  20. Murli says:

    we want to prevent duplicate entries in three columns combined, using data validation, i.e. say, column A has first name and Column B has middle name, Column C has last name. the first name can be duplicate, middle name can be duplicate, last name can be duplicate, but not all three at the same time.

  21. Murli says:

    I want to prevent duplicate entries in three columns combine, using data validation, i.e. say, column A has first name and Column B has middle name, Column C has last name. the first name can be duplicate, middle name can be duplicate, last name can be duplicate, but not all three at the same time.

  22. KokTiong says:

    Hi, I've tried above validation method to prevent duplicate value from entering into the cells. It's work, when user key in the data into the selected range. However, it's not working when user copy-&-paste the info into the same range.

    Please advice. Thanks. 

  23. ZAMEER SHAIKH says:

    Hi Chandoo,
    Does it work in Excel 2007?
    Please Reply

  24. mahavir says:

    thanks chandoo........

  25. SUSHOBH says:

    it does not work when data is copy pasted...any solution for this??

  26. shaloo says:

    hi i m shaloo and i want to know in excel if i write duplicate no.then it says or show about we are write duplicate no.

  27. Kris says:

    Hi Chandoo

    I've tried using this with a Named Range, which is actually a column in a Table as DV wont accept a table reference, and it wont work.
    Also tried using Offset to specify the Named Range, but that wont work either.

    Is it possible to use Named Ranges with DV?


  28. Paula says:

    I have tried the above formula on a table column. The Error box does not pop up, there is only the small ! next to the cell with the duplicate. The column I am working with is formulas that produce a date. Is the reason it doesn't work that the cells contain formulas rather than data?

  29. Ken says:

    The formula works but only if I enter data in cell above it. So for example, if I have "123" in B11 it does not allow me to enter "123" in B10, B9, B8, etc. But I can still enter "123" in B12. Please help! 🙂

  30. Karan says:

    Great tip.. thanks a lot

  31. I have 21 years of experience working as data entry assistant. I constantly read several blogs to keep myself up-to-date with the advances in data entry profession. I really enjoyed this blog post. From my several years of experience, I agree with you 100% when you say, “ We all know that data validation is a very useful feature in Excel. You can use data validation to create a drop-down list in a cell and limit the values user can enter. ”

    Keep blogging. I will come here again.

    --data entry assistant

  32. HaroonRashid says:

    This is really very helpful.
    Thank you

  33. Junaid says:

    how can i assign two validation on a single cell
    one is for list validation (means the data should be from that range)
    second i want to prevent them from repetition

    how can i do this ?
    P7 to P506 have GR# which are for list
    i want to prevent C column to not to repeat and should be from the P column

  34. Gaurav says:

    friend can any one tell me the formula
    exname location qty
    gaurav 1 1
    rofan 2 5
    sandeep 3 6
    gaurav 4 3
    rofan 5 4
    sandeep 6 8
    gaurav 7 9

    If this is a data.
    if i want a formula by which if i type gaurav then all the location and qty should be shown in a new page.
    i had 5,00,000 sku so if i punch one name i can get the entire details

  35. Gaurav says:

    please explain

  36. MD. RASEL SARDER says:

    THANK YOU!!!!!

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