How long will your experiment take?

How many eligible visits do you have per day?

This is the number of people visiting your site that could see the change on a given day.

What percentage of visits will see the change?

Visits per day seeing the change: 50000

What is your current conversion rate?

This is the percentage of your eligible visitors that currently complete your goal (e.g. purchasing or signing up).

Converting visitors per day: 4000

How will you change conversion?

This is the percent by which you predict you will change your base conversion rate. Use the minimum that would be worth the effort, or play with different values.
Conversion in the treatment group: 4.04%
Total daily conversions with the treatment rate: 4040
Change in daily conversions: +40

How confident do you want to be of this?

In the case that there really is no effect, there is a 5% probability that you will think there is one anyway due to random chance.

How likely should you be to detect the change?

In the case that the effect is real, there is a 20% chance that your experiment will fail to see it.

You should run this experiment for 76 days.