Regex For GST Identification Number (GSTIN)

What is the regex for the GST number in India. You can read more about the GST numbers from https://cleartax.in/s/know-your-gstin On a summary level the number is represented as L

Solution 1:

Here is the regex and checksum validation for GSTIN

\d{2}[A-Z]{5}\d{4}[A-Z]{1}[A-Z\d]{1}[Z]{1}[A-Z\d]{1}

Format details

1. First 2 digits of the GST Number will represent State Code as per the Census (2011).
2. Next 10 digits will be same as in the PAN number of the taxpayer.
   • First five will be alphabets
   • Next four will be numbers
   • Last will be check code
3. The 13th digit will be the number of registration you take within a state i.e. after 9, A to Z is considered as 10 to 35 .
4. 14th digit will be Z by default.
5. Last would be the check code.

---

Here is the code for verifying/validating the gstin number using the checksum in js

function checksum(g){
    let regTest = /\d{2}[A-Z]{5}\d{4}[A-Z]{1}[A-Z\d]{1}[Z]{1}[A-Z\d]{1}/.test(g)
     if(regTest){
        let a=65,b=55,c=36;
        return Array['from'](g).reduce((i,j,k,g)=>{ 
           p=(p=(j.charCodeAt(0)<a?parseInt(j):j.charCodeAt(0)-b)*(k%2+1))>c?1+(p-c):p;
           return k<14?i+p:j==((c=(c-(i%c)))<10?c:String.fromCharCode(c+b));
        },0); 
    }
    return regTest
}

console.log(checksum('27AAPFU0939F1ZV'))
console.log(checksum('27AASCS2460H1Z0'))
console.log(checksum('29AAGCB7383J1Z4'))

GST regex and checksum in various programming languages

Solution 2:

Here is the regex that I came up with:

/^[0-9]{2}[A-Z]{5}[0-9]{4}[A-Z]{1}[1-9A-Z]{1}Z[0-9A-Z]{1}$/

According to H&R Block India GSTIN guide, the 13th 'digit' (entity code) is "an alpha-numeric number (first 1-9 and then A-Z)". That is, zero is not allowed and A-Z represent 10-35. Hence the [1-9A-Z] is more accurate than [0-9].

The last digit, "check digit", is indeed alphanumeric: [0-9A-Z]. I have independently confirmed by obtaining and testing actual GSTINs.

Solution 3:

The correct validation for GSTIN should be

^([0][1-9]|[1-2][0-9]|[3][0-7])([a-zA-Z]{5}[0-9]{4}[a-zA-Z]{1}[1-9a-zA-Z]{1}[zZ]{1}[0-9a-zA-Z]{1})+$

The first 2 digits denote the State Code (01-37) as defined in the Code List for Land Regions.

The next 10 characters pertain to PAN Number in AAAAA9999X format.

13th character indicates the number of registrations an entity has within a state for the same PAN.

14th character is currently defaulted to "Z"

15th character is a checksum digit

This regex pattern accommodates lower and upper case.

Solution 4:

To add to above answers, this answer also provides code snippet for checksum digit

public static final String GSTINFORMAT_REGEX = "[0-9]{2}[a-zA-Z]{5}[0-9]{4}[a-zA-Z]{1}[1-9A-Za-z]{1}[Z]{1}[0-9a-zA-Z]{1}";
public static final String GSTN_CODEPOINT_CHARS = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
public static String getGSTINWithCheckDigit(String gstinWOCheckDigit) throws Exception {
            int factor = 2;
            int sum = 0;
            int checkCodePoint = 0;
            char[] cpChars;
            char[] inputChars;

            try {
                if (gstinWOCheckDigit == null) {
                    throw new Exception("GSTIN supplied for checkdigit calculation is null");
                }
                cpChars = GSTN_CODEPOINT_CHARS.toCharArray();
                inputChars = gstinWOCheckDigit.trim().toUpperCase().toCharArray();

                int mod = cpChars.length;
                for (int i = inputChars.length - 1; i >= 0; i--) {
                    int codePoint = -1;
                    for (int j = 0; j < cpChars.length; j++) {
                        if (cpChars[j] == inputChars[i]) {
                            codePoint = j;
                        }
                    }
                    int digit = factor * codePoint;
                    factor = (factor == 2) ? 1 : 2;
                    digit = (digit / mod) + (digit % mod);
                    sum += digit;
                }
                checkCodePoint = (mod - (sum % mod)) % mod;
                return gstinWOCheckDigit + cpChars[checkCodePoint];
            } finally {
                inputChars = null;
                cpChars = null;
            }
        }

Source: GST Google Group Link, Code Snippet Link

Solution 5:

Try this. It is working as per GSTIN.

^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$