We take your coupon offline when the budget is 80% utilized, and we allocate the remaining 20% to cover for possible redemptions from customers who have already clipped the coupon. For customers to have the best experience with coupons, we allow them to redeem coupons for a window of approximately 30 minutes after we disable the discovery of a coupon.
If 20% of your budget doesn't cover the customer redemptions in this 30 minute window, you might see your spend exceed your budget. The risk of your spend overshooting your budget decreases for higher budget amounts. For budgets under $10,000, you might expect a spend overshoot up to 15% (or more) of your budget.