---
description: Mastercard response code 51 means insufficient funds or over credit limit. Learn how to handle this decline using Merchant Advice Codes (MAC) and retries.
title: Mastercard Decline Code 51: Insufficient Funds
image: https://cdn.smartretry.com/cdn-cgi/image/width=1200,height=630,quality=85,fit=cover/https%3A%2F%2Fcdn.smartretry.com%2F_next%2Fstatic%2Fmedia%2Fog-image.0z0q4_5kazzzo.jpeg
---

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Mastercard

# Mastercard Issuer Response Code 51: Insufficient funds/over credit limit

soft decline

Last updated: September 25, 2026

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Table of Contents

## About 51 \- "Insufficient funds/over credit limit"

## Key details

Brand

![Mastercard](https://cdn.smartretry.com/cdn-cgi/image/width=256,quality=75,format=auto,fit=cover/https%3A%2F%2Fcdn.smartretry.com%2Fpayment-providers%2Flogos%2Fmastercard.svg)

Code

51

Category

Issuer Response Codes

Response

51

Detailed Response

Insufficient funds/over credit limit

soft decline

## What it means

Mastercard response code 51 is an issuer authorization response indicating that the cardholder's available bank account balance or remaining credit limit is inadequate to cover the transaction amount. Delivered in ISO 8583 Data Element 39, this code flags a funding shortage but does not inherently specify whether the condition is temporary or permanent.

## Classification & retryability

softRetryable: conditional

Do not automatically retry code 51 immediately. Base your retry strategy on the accompanying Merchant Advice Code (MAC), such as waiting 72 hours for MAC 02, or specific intervals like 24 hours for MAC 25\. If MAC 03 is returned, do not retry.

## Why does code 51 occur?

* The cardholder's checking or deposit account balance is lower than the requested purchase amount.
* The customer has reached or exceeded the maximum allowed credit limit on their credit card.
* Unexpected holds or pending authorizations have temporarily reduced the cardholder's available funds.

## How to solve 51?

To resolve this decline, inspect the authorization response for a Merchant Advice Code (MAC). If a MAC is present (such as 02 for 72 hours, or 24-30 for specific intervals ranging from 1 hour to 10 days), schedule an intelligent retry according to that exact timeframe. If MAC 03 is returned, treat it as a hard decline and do not retry, as doing so risks penalty fees. Without a MAC, pause automatic retries and prompt the customer to either add funds to their account or provide an alternative payment method.

### Solving as a merchant

Review your payment gateway responses for Mastercard Merchant Advice Codes to determine the exact retry window for code 51\. Implement logic to pause automatic retries if no MAC is provided, or if MAC 03 (do not retry) is returned. Present a generic, helpful decline message to the customer during checkout instead of exposing the raw raw response code, and request an alternate card.

### Solving as a customer

Review your available account balance or available credit limit to ensure adequate funds exist for the purchase. Add funds to the account, pay down your credit balance, or select a different payment method to complete the checkout.

💡Tip from SmartRetry When retries are permitted by the issuer's guidance, schedule follow-up attempts around standard payroll or direct-deposit windows—such as Friday mornings or month-end—rather than immediate re-attempts, which can trigger network fatigue and excessive retry fees.

[See the full list of Mastercard's decline codes \>](/payment-providers/mastercard#statuses)[Find code on Mastercard's website \>](https://developer.mastercard.com/mastercard-send-disbursements/documentation/response-error-codes/network-response-codes/)

### Frequently asked questions about this topic

Can I immediately retry a Mastercard decline code 51?

No, you should avoid immediate repeated authorization attempts. A retry should only be initiated if you have evidence that funds have been added, or if a Merchant Advice Code (MAC) explicitly provides a safe retry window.

What do the Merchant Advice Codes (MAC) mean when returned with code 51?

MACs dictate your retry strategy for insufficient funds. MAC 02 recommends retrying after 72 hours, while MACs 24 through 30 dictate intervals from 1 hour to 10 days. MAC 03 explicitly instructs you not to retry the transaction.

Are there penalties for retrying response code 51 too many times?

Yes. If you repeatedly retry a code 51 transaction—especially if you ignore a MAC 03 'do not retry' instruction—Mastercard may assess penalty fees for excessive and invalid authorization attempts.

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## Related codes

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