Discount and proration calculator

What it calculates

Proration charges a customer only for the part of a billing period they use. It comes up when someone joins mid-month, cancels early or changes plan before the cycle ends. Discounts reduce the price before tax.

The formula

• Percent discount = price x percent / 100, net = price - discount
• Flat discount is capped at the price
• Prorated charge = price x days used / days in period
• Plan change: credit = old price x days left / period, charge = new price x days left / period, net = charge - credit

Worked example

Upgrade halfway through a 30-day month

1. A Rs 3,000 plan with a 15 percent discount costs 3,000 - 450 = Rs 2,550
2. Upgrade from Rs 3,000 to Rs 6,000 with 15 of 30 days left
3. Credit for unused old plan = 3,000 x 15 / 30 = Rs 1,500
4. Charge for the new plan = 6,000 x 15 / 30 = Rs 3,000
5. Net due now = Rs 1,500

Questions