How do monthly subscriptions work?

After sign up, you can upgrade to the following monthly plans:

• $4.99/month ($3.99/month if billed yearly): 7,000 credits/month
• $9.99/month ($8.33/month if billed yearly): 16,000 credits/month
• $29.99/month ($24.99/month if billed yearly): 55,000 credits/month
• $49.99/month ($41.66/month if billed yearly): 100,000 credits/month
• $99.99/month ($83.33/month if billed yearly): 220,000 credits/month

These plans give you access to larger image quotas that renew automatically each month. After purchasing a monthly subscription, the billing happens automatically each month (or year if you want to be billed yearly) until you decide to cancel your payments. No headaches. :)