So, You want to create a subscription as a service app. In this article, We are going to create a simple data model for sass app.

Your clients

Client
------
Client ID
Name
...

Your plans (you can define new plans when you want). I add a Price_per_year if you want to propose a discount if the client buys 12 months in one shot (but it's only an idea).

Plan
------
Plan ID
Name
Credits_per_month
Price_per_month
(Price_per_year)

Your subscriptions

Subscriptions
------
Subscription ID
Client ID
Plan ID
Subscription_start_timestamp
Subscription_end_timestamp

Considering this model I would use 1 row per client per plan.

When a client subscribes to an offer like "Premium with 1st month free !", your database would look like this :

Client
------
ID: 1; LastName: Foo; ...

Plan
------
ID: 1; Name: Premium; Credits: -1 (unlimited); Price_per_month: 30
ID: 2; Name: Premium 1st month offer; Credits: -1; Price_per_month: 0

Subscription
------
ID: 1, Client ID: 1, Plan ID: 2, Start: 2014-05-07 08:00, End: 2014-06-06 07:59
ID: 1, Client ID: 1, Plan ID: 1, Start: 2014-06-07 08:00, End: 9999-12-06 07:59

When a client unsubscribe the 1st July, update the column end in your Subscription table with the month and the year only (because you have pre-set the day and the time).

Subscription
------
ID: 1, Client ID: 1, Plan ID: 2, Start: 2014-05-07 08:00, End: 2014-06-06 07:59
ID: 1, Client ID: 1, Plan ID: 1, Start: 2014-06-07 08:00, End: 2014-07-06 07:59

To know if a client is not unsubscribe, you could use this :

Select Count(client.*) From Client client
Inner Join Subscription sub On sub.client_id = client.id
Where DATE_TODAY Between sub.start And sub.end

Make sure that you can't have 2 subscriptions for a client at the same time.

This allow you to handle automatically the monthly subscription in your app, but not with your bank/paypal account.

But some banks offer you two services: - Unique debit - Periodic debit

The second one would allow you to handle the monthly subscription.

I would have a Purchase table

Purchase
--------
Purchase ID
Subscription ID
Payment method
...