There are two ways to enter revenue into your Flippa listing: manually entering monthly revenue and cost information, and using Google AdSense to automatically fill in the revenue section.
Manually entering monthly figures
You'll be able to enter monthly revenue figures for each full month of the last year. If your site has been established for less than a year, you'll be able to enter revenue figures for those months only, as long as your site has been live for at least two months.
If your costs are minimal (if, for example, you only pay for your domain registration and hosting), you have the option of entering a yearly figure instead of a per-month breakdown.
Using Google AdSense to enter revenue figures
If you use AdSense advertising, you can use your Google account to fill in your listing's revenue section. Read more about Verified AdSense on Flippa.