You control how recurring or one-time coupons impact your MRR in Stripe Billing. You can decide to subtract recurring discounts from MRR, subtract one-time discounts from MRR, or both. You can do this from the Billing overview page using the Configure button. These settings will apply to subscription level coupons, line-item level coupons, and stacked coupons.

Note that permanent recurring discounts are always subtracted from MRR.

Below you can see a screenshot of the options in the Dashboard.