OTP, TOTP, and HOTP: What’s the Difference?

The login process typically feels instant to the user, but behind that simplicity is a carefully chosen authentication method. 

One-time passwords are a big part of that choice, and they fall into two fundamentally different categories: TOTP and HOTP.

OTP is the broad concept: a temporary code used to verify a user or approve an action. TOTP and HOTP are simply different ways of generating that code. 

In this article, we’ll break down how OTP, TOTP, and HOTP differ, how they’re typically used together in modern multi-factor authentication, and how to choose the right method based on where a user is in their authentication journey.

What Is an OTP?

An OTP (one-time password) is a temporary code used to verify a user or approve a specific action. Unlike a static password, an OTP is valid only once or for a short period of time, limiting the risk of interception.

Static passwords are reused, stored, and often exposed through phishing or data breaches. But with OTPs, each attempt requires a new code, and expired codes are useless to hackers.

Because of this, OTPs are commonly used across key moments in the authentication flow, including login verification, new user onboarding, and sensitive account actions like password resets or security changes. Anywhere trust needs to be confirmed in real time, OTPs provide a simple but effective safeguard.

How OTPs Work

From the user’s perspective, an OTP flow looks simple. A code is received, entered, and verified. Behind the scenes, however, OTP systems are built on two distinct layers: generation and delivery.

This separation helps explain why some OTP methods feel more reliable, more secure, or more convenient depending on the situation.

OTP generation

OTP generation is the process of creating the one-time code itself. Most modern systems use algorithm-based generation rather than pure randomness.

At a high level, these algorithms combine a shared secret with a changing input, such as time or a counter, to produce a code that both the server and the user can independently generate and verify. This allows the system to validate the OTP without storing the actual code.

OTP delivery

OTP delivery is how the generated code reaches the user. Common delivery channels include SMS OTP, WhatsApp OTP, Telegram OTP, and other messaging apps, voice calls, and authenticator apps.

The choice of delivery method affects both accessibility and reliability. SMS OTPs, for example, work on just about any phone and are especially useful for onboarding and account recovery. Authenticator apps, meanwhile, don’t rely on mobile networks and are ideal for frequent logins on trusted devices. Because generation and delivery are separate layers, the same OTP logic can support multiple delivery channels depending on the use case.

What Is HOTP?

HOTP (HMAC-based one-time password) is a method used to generate one-time passwords using a shared secret and a counter. Each time a new code is generated, the counter increases, which ensures that every OTP is unique.

Simply put, HOTP works by combining a secret key with a number that moves forward one step at a time. Both the system and the user’s device track this counter. When a code is generated, they independently calculate the same value and compare the results to verify the user.

Because HOTP relies on a counter rather than time, codes do not expire automatically. A code remains valid until it is used or until the counter advances. This makes synchronization especially important. If the counter on the user’s device and the server fall out of alignment, authentication can fail until the system resynchronizes.

HOTP is commonly used in event-based scenarios where codes are generated only when requested, rather than on a fixed schedule. It is suitable for low-frequency authentication or situations where users may not be able to enter a code immediately.

What Is TOTP?

TOTP (time-based one-time password) is a method for generating one-time passwords using time as the changing factor. Instead of relying on a counter, TOTP creates a new code at fixed intervals, usually every 30 seconds.

These short-lived codes refresh automatically. Both the system and the user’s device use the current time and a shared secret to calculate the same OTP independently. As long as their clocks are in sync, the code can be verified without being sent from the server.

Since TOTP codes expire quickly, they significantly reduce the risk of reuse. Even if a code is intercepted, it becomes invalid within seconds. This makes TOTP especially effective for frequent logins and routine authentication, where users need a steady stream of secure, short-lived codes.

TOTP is commonly used by authenticator apps, which generate codes locally on a user’s device and do not depend on mobile networks. This makes it a reliable option for everyday authentication once a user has an established, trusted device.

HOTP Vs TOTP

HOTP and TOTP both generate one-time passwords, but they do so in different ways, which affects how they’re used and maintained.

HOTP creates a new code each time one is requested. It relies on a counter that moves forward with every generated OTP. The system and the user’s device must both track that counter accurately. If too many codes are generated without being used, the counters can drift, requiring resynchronization. This makes HOTP better for situations where codes are generated only when needed.

TOTP generates codes automatically based on time. A new code appears every few seconds and expires shortly after. Instead of tracking counters, the system only needs clocks to stay roughly in sync. This eliminates the need for manual resynchronization and works well for frequent logins where users expect rotating codes.

OTP Vs TOTP: Why This Comparison Is Misleading

When it comes to OTP vs TOTP, the comparison doesn’t make sense. This confusion doesn’t come from the technology itself, but from how these terms are used interchangeably in product discussions, documentation, and technical forums.

The key issue is that OTP is not a single method. It is a broad label that covers different ways of producing one-time codes, and TOTP happens to be one of those ways. In other words, all TOTPs are OTPs, but not all OTPs are TOTPs.

OTP is about purpose, not mechanics.

OTP describes the purpose of the code. It is meant to be temporary and single-use. That purpose stays the same regardless of how the code is created.

TOTP describes the mechanics. It explains how the code changes over time and how long it remains valid.

When these ideas are mixed together, it creates the impression that you must choose one over the other, when in reality, you are choosing a generation method for a specific situation.

Where SMS and WhatsApp OTP Fit

With the rise of authenticator apps and TOTP, it might seem like messaging-based OTPs should no longer be necessary. But that’s not the case. SMS and WhatsApp OTPs continue to play a critical role because they address situations that app-based methods simply cannot cover on their own.

Even highly secure systems need a way to interact with users before any trust is established and after trust is temporarily lost. Messaging-based OTPs fill that gap.

They are still widely used because they offer:

• Immediate access without prior setup
• Compatibility with nearly all phones
• A recovery path when trusted devices are unavailable

Onboarding and first-time verification

When a user signs up for the first time, there is no trusted device yet. Asking them to use an authenticator app at this stage assumes they have already installed it and are willing to complete extra steps before seeing any value.

Messaging-based OTPs prevent that friction. Sending a code via SMS or WhatsApp allows you to confirm control of a phone number immediately, using a channel the user already knows how to use. This makes it the most practical option for first-time verification.

This is why many authentication flows follow a pattern where messaging-based OTPs are used during onboarding, and app-based methods are introduced later, once the user relationship is established.

Account recovery and device changes

Account recovery is where the limits of TOTP become most visible. If a user loses their phone, deletes their authenticator app, or switches devices without migrating credentials, TOTP alone cannot help them regain access.

In these cases, out-of-band verification becomes essential. SMS or WhatsApp OTPs provide a way to re-verify the user using a channel that is independent of the lost device. Without this option, recovery often requires manual support processes, which are inconvenient and frustrating for both users and businesses. This is why even systems that prefer TOTP still keep messaging-based OTPs as a fallback. 

How Modern MFA Uses These Methods Together

Modern authentication rarely relies on a single factor. Instead, hybrid MFA is the standard approach, combining different OTP methods based on where the user is in their lifecycle.

TOTP is typically used for routine authentication on trusted devices. Authenticator apps generate time-based codes that refresh automatically, making them ideal for frequent logins without relying on mobile networks.

SMS and WhatsApp OTPs support critical lifecycle moments. They are used during onboarding, account recovery, and high-risk actions, when a trusted device may not exist or may no longer be available.

By using TOTP for everyday access and messaging-based OTPs for first-time and recovery scenarios, modern MFA systems remain secure without locking users out when circumstances change.

How to Choose the Right OTP Method

Choosing the right OTP method is usually about combining options rather than selecting just one.

Your user base is a key factor. Global or non-technical users often require SMS or WhatsApp OTPs for accessibility, while TOTP works best once users are set up with authenticator apps. Risk level also matters. Higher-risk actions often justify additional or fallback verification.

Compliance requirements and regional reach further shape these decisions. TOTP offers strong routine authentication, while messaging-based OTPs provide reach and recovery when devices or apps are unavailable.

In practice, most products use more than one OTP method. The goal is not to pick a “best” option, but to match the method to the moment.

The Difference Between OTP, TOTP, and HOTP

To conclude, OTP is the general concept of using a one-time code to verify a user or action. TOTP and HOTP are specific ways of generating those codes, each designed for different situations.

TOTP uses time-based expiration, making it practical for frequent, routine authentication on trusted devices. HOTP relies on counters, which makes it better for event-driven scenarios where codes are generated only when needed. Messaging-based OTPs, delivered through SMS or WhatsApp, support onboarding, recovery, and moments when trusted devices are unavailable.

Rather than replacing one another, these methods are meant to work together. Modern authentication systems use multiple OTP approaches to stay secure, flexible, and usable across the entire user journey.

Frequently Asked Questions

What is the difference between OTP, TOTP, and HOTP?

OTP is the general concept of a one-time password. TOTP and HOTP are specific methods for generating OTPs. TOTP uses time-based expiration, while HOTP uses a counter that advances with each code.

Is TOTP more secure than OTP?

TOTP is a type of OTP, not a replacement for it. Its short expiration window can reduce the risk of reuse, which makes it ideal for frequent logins, but security depends on how OTPs are used, not just how they are generated.

When should businesses use SMS OTP instead of TOTP?

SMS OTP is most useful during onboarding, account recovery, and high-risk actions, especially when users do not yet have a trusted device or access to an authenticator app.

Can OTP be delivered through WhatsApp?

Yes, OTPs can be delivered through WhatsApp, which is widely used in many regions and can offer better deliverability than SMS in certain markets.

Is HOTP still used in modern authentication systems?

Yes. HOTP is still used in event-based or low-frequency authentication scenarios where time-based expiration is not ideal.

Can SMS OTP and TOTP be used together in MFA?

Yes. Many modern MFA systems combine TOTP for routine authentication with SMS OTP for onboarding, recovery, or exceptional cases.

Why is SMS OTP still required for account recovery?

Because account recovery often happens when a trusted device or authenticator app is unavailable. SMS OTP provides an independent way to re-verify the user.

Which OTP method is best for onboarding new users?

SMS or WhatsApp OTPs are usually the best option for onboarding because they work immediately without requiring users to install or configure additional apps.