Ask HN: How to keep track of my online ad?

This is really all that matters. The only thing I'd add is that for you to be able to accurately gauge the success of a given campaign requires that you understand what the lifetime value (LTV) of a customer is. If, for example, you don't know your LTV, then you can make critical errors. Let's say that you spend $100 on a campaign and get 12 signups and $50 immediate money. On the surface, it appears this is a bad campaign - after all, you've lost $50. But if the LTV of each member is $12.50 and you've added 12 new members, you're LTV amount is actually $150 thus making this a $50 profit. Sure, maybe it takes six weeks or five years to get that money but, if your LTV number is close to accurate, then you can rest easy knowing that you should renew the ad campaign.