MailChimp is a “free forever” program, as long as you’ve got fewer than 2,000 subscribers managed in all lists in an account. There is a monthly send limit of up to 12,000 emails per month. And it’s all free.
So why pay for an account? A paid account offers additional features, plus you can remove the MailChimp badge from the footer of your newsletters. If you plan on sending more than 12,000 emails per month, you’ll need paid account for that.