Two-factor authentication (2FA) has become an essential part of digital security. Whether you’re logging into your Google account, online bank, or other sensitive services, a second form of authentication—often in the form of a time-based one-time password (TOTP) from an authentication app or a short numeric code received via SMS—is now standard. But how long are these codes actually valid for? Understanding the time constraints of these codes is vital for maintaining security while ensuring accessibility.
TL;DR
Authentication codes from apps like Google Authenticator are typically valid for 30 seconds before expiring and regenerating. In contrast, SMS-based authentication codes usually have a validity of 5 to 10 minutes, depending on the service provider. While TOTPs are time-synchronized, SMS codes may remain valid until used once or until their time expires. Always use your code as soon as possible to avoid issues.
How Do Authentication Codes Work?
Authentication codes are a core component of multi-factor authentication (MFA). They serve as the second layer of verification after entering your password, making unauthorized access more difficult even if your primary credentials are compromised.
- App-generated Codes (TOTP): These are created using an algorithm that generates short numeric codes at fixed time intervals based on a shared secret key and the current time.
- SMS-based Codes: Sent to your mobile number, these are temporary codes that verify your identity during the login or transaction process.
Both methods have benefits and limitations, and their usage often depends on user preferences or the policies of the services using them.
Validity Period of Google Authenticator and Similar Apps
Authentication apps like Google Authenticator, Microsoft Authenticator, and Authy use the TOTP (Time-Based One-Time Password) algorithm, standardized under RFC 6238. This means that the code:
- Is usually valid for 30 seconds.
- Automatically refreshes at the end of each interval.
- Is synced to the time clock of the device generating it—making accurate device time critical.
If you experience authentication failures with such apps, check that your phone or device clock is synchronized. Many apps provide a feature to correct time if it’s slightly off.
Why Only 30 Seconds?
The short validity restricts the time an attacker would have to misuse a stolen or intercepted code, while still giving users enough time to enter it. This tight window significantly boosts security without adding too much inconvenience.
Even if a threat actor obtains a TOTP code, it’s almost unusable within seconds if not acted upon swiftly, decreasing vulnerability to certain types of attacks.
Validity Period of SMS Authentication Codes
SMS-based codes, on the other hand, are not standardized in the same way and can vary based on the service, carrier, and security settings. However, some general rules apply:
- SMS codes are usually valid for 5 to 10 minutes.
- Some services invalidate the code immediately after it’s used—even if that’s within seconds of being sent.
- The timestamp is often embedded or tracked by the service backend.
This longer validity window accounts for potential delays in SMS delivery—especially in areas with erratic mobile signal or server congestion.
Are SMS Codes Less Secure?
Yes. Experts increasingly recommend using app-based methods due to:
- SIM swapping attacks: where attackers gain control of your mobile number.
- SMS interception: via spyware or unsecured communication channels.
- Lack of encryption in the SMS protocol makes it prone to interception.
That said, SMS is better than no two-factor authentication at all. It’s widely supported and can still be useful if app access is unavailable.
What Happens if You Enter an Expired Code?
If you attempt to log in with an expired code, most services will simply reject the attempt and prompt you to enter a new one. You’ll likely need to:
- Wait for a new TOTP to be generated (if using an app).
- Request another SMS code (if using SMS authentication).
Some systems have a built-in tolerance window of a few seconds or even one previous code for backward compatibility. However, this is rare and not recommended for high-security environments.
How to Ensure Your Codes Are Valid When Entering Them
To increase your success rate when entering authentication codes:
- Enter the code immediately after it appears on your app.
- Make sure your device clock is automatically synced—manually set times can cause issues with TOTPs.
- If using SMS, be ready to input the code as soon as it arrives.
Also, if you’re using a desktop and reaching for your phone, have the code app open beforehand to save time.
Server-Side Validity Tolerance
While TOTPs are strictly 30 seconds in duration, some server implementations may offer “clock skew tolerance” to prevent authentication failures due to slight time differences. For example:
- A service may accept the code from the previous or next time window in addition to the current one.
- This results in a total possible window of up to 90 seconds in rare cases.
However, this is not always implemented. Therefore, assuming a 30-second life span for app-generated codes is the most secure approach.
Can You Extend the Life of a Code?
No. Codes are generated based on strict timing or expiration parameters and cannot be extended. If a service allows retries with the same code beyond the default validity period, it is an exception, not the norm. Attempting to reuse a code is generally a sign of outdated client-side tech or misconfigured systems and should raise security concerns.
Security Best Practices with Auth Codes
To maintain security while using either method, follow these key principles:
- Enable app-based authentication over SMS where possible.
- Keep your device’s time accurate using automatic syncing with internet time servers.
- Never share your authentication code with anyone, even if they claim to be tech support.
- Check for phishing attempts—be cautious of fake login prompts.
And always assume urgency: codes are short-lived for a reason, so treat them like digital fuses set to detonate after a defined time.
Conclusion
Digital authentication codes—whether from Google Authenticator or sent through SMS—are governed by short validity windows for security purposes. TOTP codes generally last 30 seconds, while SMS codes may remain valid for up to 10 minutes. The goal is to reduce the time window in which malicious actors can misuse these credentials.
While both methods add layers of protection, app-based authentication remains the more secure and preferred method. Make a habit of using the codes as soon as they arrive, keeping your devices up-to-date and time-synced, and being wary of potential threats. Ultimately, safeguarding your digital life begins with understanding how your tools protect you—and the limitations they carry.
