Subscription proration explained, with worked rand examples

Subscription proration means charging or crediting a customer only for the part of a billing period they actually used on each plan when they change plans mid-cycle. If a customer upgrades halfway through the month, they pay roughly half of the difference between the old and new price for the rest of that month, and the full new price from the next renewal.

Proration sounds simple, but the details (days or seconds, credits or refunds, invoice now or later) cause a surprising number of billing queries. This guide sets out the options and walks through the calculations.

When subscription proration applies

Proration usually comes into play when:

• A customer upgrades to a more expensive plan mid-cycle.
• A customer downgrades to a cheaper plan mid-cycle.
• A customer adds or removes seats or quantity-based add-ons.
• You move a customer's billing date, for example to align all accounts to the 1st of the month.
• A subscription starts mid-month and you want every customer to renew on the same date.

It does not normally apply to free trials (nothing has been charged yet) or to cancellations, where most businesses simply let the paid period run out.

The basic formula

For a plan change on a given day:

1. Unused value of the old plan = old price × (days remaining ÷ days in period)
2. Cost of the new plan for the rest of the period = new price × (days remaining ÷ days in period)
3. Amount due now = (2) − (1)

If the result is positive, the customer owes that amount. If it is negative, the customer has a credit.

Some systems calculate to the second rather than to the day. Day-based proration is easier for customers to check, which usually means fewer support tickets.

Worked example 1: upgrade mid-month

• Current plan: Starter, R300.00 per month (VAT inclusive)
• New plan: Growth, R600.00 per month (VAT inclusive)
• Billing period: 1 to 30 June (30 days)
• Upgrade date: 16 June, leaving 15 days

The customer pays R150.00 on 16 June and R600.00 on 1 July.

On the tax invoice for the R150.00, the VAT included is R150.00 × 15/115 = R19.57, with R130.43 excluding VAT.

Worked example 2: downgrade mid-month

Now the reverse: Growth at R600.00 down to Starter at R300.00 on 16 June.

You now have three options:

1. Credit the next invoice. The 1 July renewal of R300.00 is reduced to R150.00. This is the most common approach.
2. Refund R150.00 to the original payment method, with a credit note.
3. Downgrade at the end of the period instead. The customer keeps Growth until 30 June and moves to Starter on 1 July, with no proration at all.

Option 3 is popular for downgrades because it is simple and avoids small refunds. Whichever you choose, if you reduce a previously invoiced amount, a VAT vendor will usually need a credit note rather than simply editing the old invoice. Our guide on credit note vs refund explains the difference.

Worked example 3: adding seats

A team plan costs R120.00 per user per month. A customer with 5 users adds 3 users with 10 days left in a 31-day month.

• Extra cost: 3 × R120.00 × 10/31 = R116.13 (rounded to the nearest cent)
• From next renewal: 8 × R120.00 = R960.00

Rounding matters: decide whether you round each line or the total, and apply it consistently so invoice totals always reconcile.

Annual plans and proration

Proration has a larger impact on annual plans because the amounts are bigger.

Suppose a customer on an annual plan of R6,000.00 upgrades to R9,600.00 with 146 days remaining in a 365-day year:

• Unused old plan: R6,000.00 × 146/365 = R2,400.00
• New plan for remaining days: R9,600.00 × 146/365 = R3,840.00
• Due now: R1,440.00

Many businesses invoice this immediately rather than waiting for renewal, because the difference is material. Our comparison of annual vs monthly billing covers other trade-offs of annual plans.

Policy decisions to make upfront

Write these down before you build or configure anything:

1. Upgrades: immediate with proration, or at next renewal?
2. Downgrades: immediate with a credit, or at the end of the period?
3. Calculation unit: days or seconds?
4. Credits: carried forward to the next invoice, or refunded?
5. Minimum amounts: do you skip charging very small prorated amounts, for example under R10.00?
6. Coupons: does a percentage discount apply to the prorated charge?
7. Collection: is the prorated amount charged immediately to the saved payment method, or added to the next invoice?

For debit order customers, an immediate mid-cycle charge may not be practical, because collections go out in scheduled batches. Adding the prorated amount to the next collection, within what the customer's mandate allows, is usually simpler.

Explaining proration to customers

Customers rarely complain about the maths; they complain about surprises. Reduce queries by:

• Showing the prorated amount before the customer confirms a plan change.
• Putting a clear line on the invoice, such as "Growth plan, 16 to 30 June (15 of 30 days)".
• Including the credit for unused time as a separate line.
• Linking to a short help article with an example like the ones above.

How CentraPoint helps

CentraPoint's subscription packages and plans let customers change plan within the rules you set, including through the customer self-service portal, and renewals are collected automatically by saved card token, debit order or invoice. Invoices are VAT-aware (tax-inclusive or exclusive) and branded, and refund notes are generated as PDFs when you do refund. To see how plans and changes are modelled, read the subscriptions docs.

Frequently asked questions

What does prorated mean in a subscription?

Prorated means the charge or credit is calculated in proportion to the time used. If a customer changes plan halfway through a period, they pay the new price only for the remaining half.

How do you calculate a prorated upgrade?

Work out the unused value of the old plan and the cost of the new plan for the remaining days, then subtract the first from the second. For example, moving from R300.00 to R600.00 with half a month left costs R150.00 now.

Should downgrades be prorated?

They can be, but many businesses apply downgrades at the end of the current period instead. That avoids small refunds and credits while still giving the customer the cheaper price from the next renewal.

How is VAT handled on prorated charges?

A prorated charge is part of the price of the supply, so VAT applies to it in the same way. For a VAT-inclusive amount of R150.00, the VAT portion at 15% is R19.57.