A sample customer has a $99 monthly subscription, 10,000 included units, and a $0.01 extra-unit rate. They use 15,000 units, have a 10% discount on base fee and overage, and hold a $20 credit.
Calculate in a defined order
- Extra units: 15,000 − 10,000 = 5,000.
- Overage: 5,000 × $0.01 = $50.00.
- Subtotal: $99.00 + $50.00 = $149.00.
- Discount: $149.00 × 10% = $14.90.
- Discounted subtotal: $149.00 − $14.90 = $134.10.
- Apply the $20 credit: $114.10 amount due, before tax.
Try the discount-and-credit sample. Change the credit or discount and generate a sample draft to compare.
Why the order matters
A discount changes the price under the customer's agreement. A credit reduces the balance still owed. Applying a percentage after subtracting a credit would produce a different result. Define which lines are discountable and when credits apply.
This sample discounts base fee and overage together, rounds the discount once half up to cents, then applies credit. A credit larger than the discounted subtotal leaves the amount due at zero and shows the remaining credit separately. It does not imply an automatic cash refund.
Taxes and payment collection are excluded. Validate coupon scope, credit balances, and tax treatment against your actual configuration before posting a production invoice.
Read about credits and adjustments and use the billing migration checklist to compare your first test invoice with your existing process.