Excel lets you sign a spreadsheet using your computer's built-in certificate or a cloud signature service

You can add a digital signature to an Excel file in three ways: using a certificate already on your computer, requesting one from a certificate authority, or using Microsoft 365's cloud-based signing feature. The method you choose depends on whether you need the signature to be legally binding, who needs to verify it, and what software the other person has access to.

The simplest route for most people is the built-in certificate method if you already have one, or Microsoft 365's cloud signing if you have a subscription. Both take about five minutes. The certificate authority route takes longer but creates a signature that works across different programs and platforms.

Key Takeaways

  • Excel's built-in signature feature uses a certificate stored on your computer, which you may already have if your workplace issued one.
  • Microsoft 365 subscribers can sign documents using their Microsoft account without needing a separate certificate.
  • Signing an Excel file locks it against further changes, so make sure the spreadsheet is final before you sign.
  • The person receiving the file needs compatible software to see and verify your signature — not all programs display digital signatures the same way.
  • A digital signature in Excel proves you signed the file and that it has not been altered since, but does not prove your identity unless you used a certificate from a recognized authority.

Signing with a certificate you already have

If your workplace or school issued you a digital certificate, it is likely already installed on your computer. Open the Excel file you want to sign and go to File > Info > Protect Document > Add a Digital Signature. A dialog box will open asking you to choose a certificate.

Select the certificate from the list — usually it will show your name or your organization's name. You can add a comment explaining why you are signing (for example, "Approved for payroll" or "Budget verified"). Click Sign. Excel will add a signature line to the file and lock it. Anyone who opens the file will see that it was signed by you and on what date.

If you do not see a certificate in the list, your computer does not have one installed. You will need to either request one from your organization's IT department or use the Microsoft 365 method instead.

Signing through Microsoft 365

If you have a Microsoft 365 subscription, you can sign without needing a certificate. Open the file and go to File > Info > Protect Document > Add a Digital Signature. Instead of choosing a certificate, select Get a Digital ID and then Sign with Microsoft 365.

You will be asked to sign in with your Microsoft account. Once you do, Excel will create a signature using your account information. This signature is tied to your Microsoft identity, so the person receiving the file can verify it came from you if they also have a Microsoft account.

This method is faster than getting a certificate from an authority, but the signature only works smoothly in Microsoft products. If someone opens the file in Google Sheets or another program, they may not see the signature or may see a warning that it cannot be verified.

Getting a certificate from a certificate authority

If you need a signature that works across different programs and is legally recognized, you need a certificate from a certificate authority — an organization that verifies your identity and issues digital credentials. Common authorities include DigiCert, Sectigo, and GlobalSign. This process takes days or weeks, not minutes.

You will need to explore through the certificate authority's website, provide proof of identity, and pay a fee (usually between $100 and $400 per year). Once approved, the authority will send you a certificate file to install on your computer. After installation, you can sign Excel files the same way as with a workplace certificate: File > Info > Protect Document > Add a Digital Signature.

This route is worth the time and cost only if you sign documents regularly and need the signature to be trusted by people outside your organization or by government agencies.

What happens to the file after you sign it

Once you sign an Excel file, the spreadsheet becomes read-only. Other people can open it and see the data, but they cannot edit the cells. If someone tries to change anything, Excel will break the signature and show a warning that the file has been modified.

This means you need to be certain the spreadsheet is correct before you sign. If you realize you made a mistake after signing, you will have to delete the signature, make the change, and sign again. To remove a signature, go to File > Info > Protect Document > Remove Digital Signatures.

How the other person verifies your signature

When someone receives your signed Excel file, they can see the signature by opening the file and looking at the Info tab. The signature will show your name, the date you signed, and whether the file has been altered since you signed it. If the file has been changed, Excel will display a warning.

If you used a certificate from a recognized authority, the other person can click on the signature to see details about the certificate and confirm it is valid. If you used a workplace certificate or Microsoft 365 signature, they may see a message that the certificate cannot be verified — this does not mean the signature is fake, only that their computer does not recognize the issuing authority.

On Mac computers, the process is similar but the menu path is slightly different: Review > Protect Sheet > Add a Digital Signature. The signature itself works the same way across Windows and Mac.

When a digital signature in Excel is not enough

A digital signature in Excel proves that you signed the file and that it has not been changed since. It does not prove your legal identity unless you used a certificate from a recognized authority. If you are signing a contract, a financial document, or anything that might be challenged in court, a signature from a certificate authority is much stronger than a workplace certificate or Microsoft 365 signature.

Some organizations and government agencies require signatures from specific certificate authorities. Before you spend time getting a certificate, check with the person or organization that will receive the document to see what they accept.

Frequently Asked Questions

Can I sign an Excel file on my phone or tablet?

The built-in signature feature is not available in Excel for mobile. If you have Microsoft 365, you can use the web version of Excel at Office.com to sign a file. Otherwise, you will need to use a computer.

What if the person receiving the file does not have Excel?

They can open the file in Google Sheets, LibreOffice, or other spreadsheet programs, but they will not see the signature or will see a message that it cannot be verified. If the signature is important, ask them to open the file in Excel or the web version of Excel.

Can I add a signature image instead of a digital signature?

Yes, but that is different from a digital signature. You can insert an image of your handwritten signature using Insert > Pictures, but this does not prove you actually signed the file or that it has not been changed. A digital signature does both.

What if I lose the certificate on my computer?

If you got the certificate from your workplace, contact your IT department — they can reinstall it. If you got it from a certificate authority, you can read it again from their website using your account. If you used Microsoft 365, your signature is tied to your Microsoft account, so you can sign from any computer where you log in.

Does signing an Excel file work the same way in Google Sheets?

No. Google Sheets does not have a built-in digital signature feature. If you need to sign a spreadsheet, you will need to use Excel or convert the file to PDF and sign that instead.