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When a Payment Bounces Back Because the Routing Number Doesn’t Add Up
When dealing with ACH payments, every digit matters. The routing number is one of the most important pieces of information in a transaction—it tells the ACH network which bank to send the funds to. If the routing number is incorrect or fails the check digit validation, the payment won’t go through.
Instead, you’ll get an ACH Return Code R42, which points to a problem with either the routing number itself or the math behind it.
Let’s break down what R42 – Routing Number or Check Digit Error means, why it shows up, and how to fix it so you can avoid future delays.
What Does ACH Return Code R42 Mean?
ACH Return Code R42 stands for:
“Routing Number or Check Digit Error.”
Here’s NACHA’s official definition:
R42 – Routing Number or Check Digit Error: The routing number included in the entry is either invalid or fails the check digit validation formula used to verify accuracy.
In simple terms: the routing number submitted doesn’t pass the math test that confirms it’s a real and valid number.
What Is a Check Digit?
Every U.S. bank routing number is 9 digits long. The last digit is called the check digit, and it’s calculated using a formula based on the first eight digits. This helps the ACH network catch typos or errors before a transaction is sent to the wrong bank.
If the check digit doesn’t match the result of the formula, the system knows the routing number is invalid—and the transaction gets returned.
What Causes an R42 ACH Return?
ACH Return Code R42 typically happens because of:
Typos in the routing number (especially in the last digit)
Copy-paste errors or manual data entry mistakes
Using the wrong routing number type (for example, a wire transfer routing number instead of an ACH routing number)
Outdated routing info after a bank merger or acquisition
Ineligible financial institutions that don’t participate in the ACH network
Even one incorrect digit can trigger an R42 return.
How to Handle ACH Return Code R42
Here’s how to resolve an R42 error quickly and correctly:
1. Review the Routing Number
Check the routing number used in the transaction. Make sure it’s 9 digits long and doesn’t contain letters or symbols.
2. Use a Routing Number Lookup Tool
There are online tools that allow you to verify whether a routing number is valid, active, and eligible for ACH processing. These tools often confirm the associated bank and whether the number passes the check digit test.
3. Contact the Customer
If you’re unsure where the error came from, ask the customer to confirm their bank’s ACH routing number (which can differ from wire or check routing numbers).
4. Update and Resubmit the Transaction
Once you have the correct routing number, update your records and resubmit the payment.
How to Prevent R42 Errors in the Future
Here are a few tips to avoid routing number errors:
Use bank account verification tools that validate routing numbers in real-time
Ask for a voided check during customer onboarding to confirm accurate bank info
Train your team to look out for common input mistakes when handling account setup
Avoid using routing numbers found on wire instructions—ACH routing numbers can be different
Keep routing info up to date, especially for customers at banks that have merged or rebranded
Routing number errors are among the easiest to prevent—and catching them before submission saves time and keeps payments flowing.
Get ACH Processing With Durango
ACH Return Code R42—“Routing Number or Check Digit Error”—means the routing number used in your transaction was invalid or failed the check digit test. It’s a fixable formatting issue, but it will stop your payment from going through until corrected.
At Durango Merchant Services, we help businesses process ACH payments accurately, reduce avoidable return codes, and streamline their billing systems. Whether you’re sending payroll, collecting invoices, or handling high-risk ACH payments, our team is here to support you every step of the way.
