Your subscription is based on a 30-day renewal cycle, and your payment will be charged every 30 days based on the delivery date of your previous order. You will not be charged on the same day each month, but instead it'll be based on your previous order's delivery date so you never miss a day of vitamins.
Each month you'll get an email "Your next order is coming up" 48 hours before your order is processed, so you won't be charged without a heads-up!