How to Fix the 'bccomp()' Undefined Function Error

When working with Magento 2, technical errors are common — especially during installation, upgrade, or custom module development. One such error is:
Fatal error: Uncaught Error: Call to undefined function bccomp()
If you've seen this message, don’t worry. It's a common problem with a simple fix. In this guide, we'll explain what causes this error and show you how to resolve it quickly.

Why Does the 'bccomp() Undefined Function' Error Occur?
The bccomp() function belongs to PHP's BCMath (Binary Calculator) extension.
Magento 2 relies on this extension to handle arbitrary precision mathematics, especially when dealing with pricing, taxes, and currency calculations.
If your PHP installation doesn't have the BCMath extension enabled, Magento can't find the bccomp() function — resulting in this fatal error.
Check if BCMath Is Installed
First, check whether the BCMath extension is installed and active on your server.
Install BCMath Extension
The installation process depends on your server's operating system. Generally, it involves using a package manager to add the BCMath extension to PHP.
Restart Your Web Server
After installing BCMath, restarting your web server is necessary to apply the changes.
This ensures that PHP recognizes the newly installed extension.
Verify BCMath Activation
Once restarted, you should double-check that BCMath is properly enabled.
This verification confirms that your Magento 2 environment is ready to go.
Additional Tip: Check Your php.ini File
If BCMath is installed but still not working, make sure it’s enabled in your php.ini configuration file.
Look for a line related to BCMath and ensure it’s not commented out.

After making changes, don't forget to restart the web server again.

The Call to undefined function bccomp() error in Magento 2 is usually a sign that your PHP environment is missing a critical extension.
By ensuring BCMath is installed and properly configured, you can fix the issue quickly and prevent similar errors in the future.

Keeping all required PHP extensions active is vital for a stable and high-performing Magento 2 store — especially when handling complex eCommerce operations.
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