The subscription 'End Date' is the day your subscription automatically renews. Each subscription lasts 30 days from the Start Date to the End Date. Subscriptions are automatically renewed on the End Date or when the allotted number of texts in the subscription are all used up.
To find your 'End Date', sign in to your Text Integration account: https://secure.textintegration.com/
In the Dashboard, on the Subscription Information box, you will see when each of your subscriptions will end under the column "End Date".
Note: The date format is DD/MM/YY.