The Tax ID Pro Team
December 1, 2022

Why Validating Tax ID Numbers is So Hard

Why Validating Tax ID Numbers is So Hard

Building a validator for tax ID numbers is hard. That's why Tax ID Pro has created an API that handles tax ID number validation for you. But if you want to try to build a validator yourself, here are a few things to keep in mind.

First, you will want to determine what countries you want to support. Each country has a unique format, so you will have to create a separate function for each country. Tax ID Pro supports over 100 countries, so if you can't narrow down your list, our service can save you days, weeks, or months of work.

Once you have your countries, the OECD provides a comprehensive list of tax ID formats. Most major economies and EU countries are represented on their website.

Validating tax ID numbers requires more than a simple test for formatting. Many formats also include a checksum algorithm. The checksum is a digit (sometimes more than one digit) that is determined by running the other digits through an algorithm such as Luhn. The checksum is more of a test for typos than a strong security feature. It is a great thing to include in your validator. Not all tax ID formats use a checksum (U.S. social security numbers, for example), but for those that do, Tax ID Pro includes a checksum test as part of its validation API.

One last tricky bit of business is figuring out when to accept multiple formats. If you expect a tax ID for an individual, you can focus on tax ID formats for individuals. Same for businesses or other entities. The Tax ID Pro API allows you to easily test multiple formats with one request.

Whether it makes more sense to roll your own validator, or use a third-party API such as Tax ID Pro, it's important to include validation for tax ID numbers, if you will need to use them for official filings. Proper validation can save you lots of time and headaches, and discourage fraud and abuse.

Tax ID Pro offers an amazing API that makes it easy to check tax ID numbers for validity. Set up a free Tax ID Pro account and discover how easy it is to integrate our validator into your software or web application.