Here is the clearest explanation of how WhatsApp blocks are calculated when you are using a normal WhatsApp/WhatsApp Business account through an unofficial API (UltraMsg, Chat-API, etc.) and what role your number’s history plays.

This is based on known Meta behaviour-detection patterns, industry data and analysis of thousands of banned numbers.

There is no single “block formula”, but Meta’s system uses weighted signals, and they combine into a risk score that triggers restrictions.

I’ll break it down cleanly.

1. Is it a percentage of messages sent?

Yes. One part of the algorithm is percentage-based, specifically:

A. Block Rate

This is the proportion of users who block your number within a short period.

Examples:

• If you send 50 messages and 3 people block you, that is 6 percent. That is considered very high.
• If you send 200 messages and 3 people block you, that is 1.5 percent. Still risky but less severe.

WhatsApp does not publish the threshold, but from observed patterns:

Block rate over 2 percent in a short window = very high risk

Even one block can trigger internal checks if your number is new or already under review.

2. It is also influenced by the ratio of your behaviour

Not just percentages. Meta looks at:

A. Outbound vs Inbound ratio

If you send a lot more messages out than you receive back, it looks like spam.

A healthy account has:

• many messages flowing in
• many users replying
• fewer messages going out than coming in

A risky account has:

• a high volume of outbound messages
• few replies
• many ignored messages

B. Time-based spikes

Sending too many messages in too short a period looks automated.

Meta detects:

• messages per minute
• bursts per hour
• unnatural timing (perfectly spaced intervals, same message to many users at once)

These create “automation flags”.

C. Message variation

If content is too similar, it increases risk.

Repetition signals:

• bot
• broadcast
• unsolicited marketing

3. The history of your number is a major factor

Your number earns a kind of “trust score” over time.

New number = extremely fragile

Any:

• spike
• block
• pattern
• high outbound ratio
• low response rate

can cause immediate review.

Aged number = more tolerant

If your number has:

• months or years of usage
• lots of organic chats
• saved contacts
• high reply rates
• low block history

…it is much harder to ban.

Old numbers with strong history get “benefit of the doubt”

This is why businesses that use a number for years with regular customer conversations can send more without issues.

Old number with poor history stays fragile

If the number has:

• many blocks in the past
• previous restrictions
• previous automation patterns
• history of mass sending

…the system “remembers” and flags sooner.

4. What actually triggers the ban is a combined score

Meta uses something like a weighted risk score, which includes:

1. Block rate

Strongest signal
Percentage based
Time-window based (recent activity counts more)

2. Engagement rate

Low reply rate = risky
High reply rate = safe

3. Message velocity

Speed of sending
Patterns in timing
Burst behaviour

4. Message similarity

Same wording to many users

5. Number age and trust level

Newer number = more sensitive
Older number = more forgiving

6. Automation footprint

Unnatural timing
Consistent intervals
Repeated patterns
Device signature mismatches

When the combined score crosses Meta’s internal threshold, the number is:

• rate-limited
• restricted
• temporarily banned
• permanently banned

depending on severity.

5. Important: Blocks are not only caused by outbound activity

Meta also checks:

A. How many people view your message but do not reply

Silent reads count as “weak engagement”.
Too many silent reads + high outbound = spam profile.

B. Session behaviour

Multiple logins
Multiple devices
API-like patterns
Session replays
Frequent reconnects

These look like bot behaviour.

6. How to calculate YOUR safe limit

Use this simple rule:

Safe hourly limit = (Total people who have replied at least once) ÷ 10

Example:

• 400 people replied before
• Safe sends per hour = 40
• 600 responders = 60
• 1200 responders = 120

This adjusts the limit to your number’s true “trust level”.

Final Summary

WhatsApp bans are based on a mix of:

• percentage block rate

• reply rate

• speed of sending

• similarity of messages

• history of previous behaviour

• number age

• engagement levels

• signs of automation

It is not one metric.
It is not just volume.
It is a combined behavioural model.

So automating WhatsApp you must stay below the behavioural thresholds because Meta expects human behaviour, not automation.