Average profit per customer in $ during desired payback period
If cash allows it, you can enter the profit over the full customer lifetime. But many companies want a payback period of 12 months or even less, so use the profit you earn from a new customer within the desired payback period.
On the cost side, it's best not include overhead costs that don't increase (much) when serving additional customers, such as office rent and salaries that won't increase (much) by acquiring new customers.
For most advertisers, 50% to 70% is the profit-maximizing range.
A higher percentage will allow you to bid more aggressively and capture more market share, but it will be at the expense of profitability.
A lower percentage will allow you to keep more of your margin, but it will be harder to compete with advertisers who are willing to invest more of their margin into acquisition.
If you set this to 100%, your advertising is breaking even.
This is the percentage of the leads from your website (usually form fills) that become paying customers.
Please note that this percentage may vary strongly by marketing channel, campaign, location, etc. so make sure to import as much advertising data as possible into your CRM.