If you change your subscription plan in the middle of a billing period, you will be charged a pro-rated amount for the rest of the billing period or your account will receive a pro-rated credit. You will be charged the full amount of the new rate on your renewal date.
If you are on one of our Per Test plans and change your plan before the 15th of the month, the test report limit of the new plan will also go into effect immediately. If you change your plan after the 15th of the month, the test report limit of the new plan will go into effect at the beginning of the following month. See our article about selecting your plan to learn more.