Can I Control How Often Each Variant Is Shown to Visitors?

Tes. By default, Nelio A/B Testing distributes visitors evenly across all variants in a test, giving each version the same chance of being shown.

Starting with Nelio A/B Testing 8.4, you can enable custom variant distribution and decide what percentage of visitors should see each variant.

For example, instead of splitting traffic equally between two variants (50% / 50%), you could configure the test so that:

• the Control receives 80% of the traffic; and
• the Variant receives 20%.

This gives you more flexibility while still allowing you to compare performance between versions.

When Should I Use Custom Traffic Distribution?

Custom traffic allocation can be useful when:

• You want to reduce exposure to a risky or experimental design
• You’re testing changes on a business-critical page
• You want to prioritize a preferred variant while still collecting data from alternatives
• You’re running tests on high-traffic websites and want more control over visitor distribution

For most tests, we recommend keeping the default equal distribution, as it usually produces statistically significant results more quickly.

How to Enable Custom Variant Distribution

To use custom traffic allocation:

1. Go to Nelio A/B Testing → Settings. Under Plugin Behavior → Variants, enable
2. Allow custom variant distribution in tests.
3. Create a new test.
4. Add your variants.
5. Specify the percentage of traffic each variant should receive
6. Save and start your test

Important Considerations

Before enabling custom traffic allocation, there are a couple of important things you should keep in mind.

Traffic Distribution Cannot Be Changed After Starting the Test

Once a test has started, its traffic distribution is locked.

This ensures the statistical integrity of the test. Changing the percentage of visitors assigned to each variant during a test would make the collected data difficult to interpret and could invalidate the results.

For this reason, make sure you review the configured percentages carefully before launching the test.

More Traffic Means Faster Results

Variants that receive a larger percentage of visitors collect data more quickly.

Conversely, variants receiving only a small share of traffic require more time to accumulate enough page views and conversions for reliable statistical analysis.

Keep this in mind when assigning very low percentages to a variant.

Advanced: How Custom Distribution Affects the nab Parameter

Normally, Nelio A/B Testing determines which variant a visitor sees by storing a value in the nabAlternative cookie and mapping it evenly across the available variants.

When custom traffic distribution is enabled, the plugin uses that stored value differently so it can honor the percentages you’ve configured.

As a result, the nab query parameter no longer maps directly to a variant number.

For example, in a two-variant test with an 80% / 20% distribution, several different nab values may correspond to the same variant.

This behavior is expected and ensures visitors are distributed according to the configured percentages.

Note: This only affects advanced integrations or debugging scenarios where you manually work with the nab query parameter. Most users don’t need to worry about this implementation detail.

🔍 Learn more: How Variant Delivery Works Internally