When modeling a subscription product, you'll often have a number of existing subscribers prior to the start of your plan. For these cases, check the Pre-existing subscribers checkbox next to the initial subscriber count.
If you uncheck this box, the initial subscriber number you enter will be modeled as new subscribers in the first month.
By default, Opstarts will spread the existing subscribers out across the prior months of the subscription period based on the growth and churn rate you enter. In this example, it's an annual subscription product, so Opstarts spreads the existing subscribers across the prior 12 months.
These values will determine when the renewal dates come up for these subscribers in your model. To customize the exact renewal dates, uncheck Default subscriber counts and enter in the total number of subscribers that were either new or renewed in each month.
In this example, this product didn't start getting subscribers until Dec 2015, so the first renewal revenue from pre-existing subscribers will be shown in Dec 2016, and so forth.