BYTETOOLS

Subscription Proration Calculator

Work out mid-cycle upgrade and downgrade amounts: unused credit on the old plan, prorated charge on the new one, net due today and the next renewal.

—
Days in the cycle
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Days remaining
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Proration factor
—
Due now
LineFull cycle amount× proration factorAmount
Unused time on the old plan (credit)———
Remaining time on the new plan (charge)———
Net amount due now———
Next renewal—full cycle—

credit = old price × remaining ÷ cycle length  ·  charge = new price × remaining ÷ cycle length  ·  due now = charge − credit

Worked example: a $10.00 monthly plan starting 1 January, upgraded to $30.00 on 16 January. The cycle is 31 days and 16 remain, so the credit is 10 × 16 ÷ 31 = $5.16, the new charge is 30 × 16 ÷ 31 = $15.48 and $10.32 is due immediately — the same numbers the major billing platforms produce for that scenario.

Day-count convention: on the whole-day basis the day of the change counts as used(it was served on the old plan), so a change on 16 January in a 31-day cycle leaves 16 remaining days, not 17. Tick “count the change day as unused” if your billing system is generous the other way. On the per-second basis the fraction is measured from the exact moment of the change instead.

Everything is calculated locally in your browser and nothing is uploaded. Monthly and annual cycles use calendar arithmetic, so a cycle starting on 31 January ends on 28 or 29 February rather than overflowing into March — which is why the number of days in a cycle changes from month to month and the same upgrade produces slightly different amounts at different times of year. Real invoices may also apply tax on top of the net amount and round each line differently; treat this as the pre-tax proration, not a billing-system replica.

What is the Subscription Proration Calculator?

When a customer changes plan halfway through a billing cycle, two amounts appear: a credit for the time they paid for and did not use on the old plan, and a charge for the time remaining on the new one.

  • Unused credit and prorated charge shown as separate lines
  • Net amount due now, or a credit when the change is a downgrade
  • Daily, weekly, monthly, quarterly and annual cycles on calendar dates
  • Seat-count changes priced alongside plan-price changes
  • Whole-day or per-second basis with a stated day-count convention
  • Next renewal date and full renewal amount

How to use the Subscription Proration Calculator

  1. 1

    Choose the currency and billing cycle, then enter the date the current cycle started.

  2. 2

    Enter the date the plan changes, and pick whole-day or per-second proration.

  3. 3

    Type the old plan price and seat count, then the new plan price and seat count.

  4. 4

    Read the credit, the new charge and the net amount due now in the breakdown table.

  5. 5

    Check the next renewal date and the full amount that will be charged then.

About the Subscription Proration Calculator

When a customer changes plan halfway through a billing cycle, two amounts appear: a credit for the time they paid for and did not use on the old plan, and a charge for the time remaining on the new one. This calculator works out both, nets them off, and tells you what is actually due today and what the next full renewal will be.

It handles daily, weekly, monthly, quarterly and annual cycles using calendar arithmetic, seat-count changes on either side, and two proration bases: whole days, or per second when the exact moment of the change matters. The day-count convention is stated plainly and can be flipped, because billing systems disagree about whether the day of the change belongs to the old plan or the new one.

Everything is calculated locally in your browser and nothing is uploaded. These are pre-tax amounts: real invoices apply tax on top and may round each line differently, so treat the output as the proration arithmetic rather than a byte-for-byte replica of any one billing platform.

Frequently asked questions

How is subscription proration calculated?

Take the fraction of the cycle still to run, then apply it to both prices: the credit equals the old price times that fraction, and the new charge equals the new price times the same fraction. A 10.00 plan upgraded to 30.00 with 16 of 31 days left gives 5.16 credit, 15.48 charge and 10.32 due today.

Does the day of the change count as used or unused?

On the whole-day basis here it counts as used, because the customer was served on the old plan that day — so a change on 16 January in a 31-day cycle leaves 16 remaining days, not 17. Tick the box to flip the convention if your billing system is more generous.

What happens when a customer downgrades mid-cycle?

The credit for unused time on the expensive plan exceeds the charge for the cheap one, so the net amount is negative. The tool shows it as a credit rather than a charge. Most billing systems hold that credit against the next invoice instead of refunding it.

Why do the same upgrade amounts differ month to month?

Because months are different lengths. A monthly cycle running from 1 February is 28 days and one from 1 March is 31, so the same mid-month change produces a different fraction of the cycle and therefore a different amount. Annual cycles do the same thing on leap years.

How are seat changes prorated?

Exactly the same way. The full cycle amount for each side is the price per seat times the seat count, and the same remaining-time fraction applies to both. Adding three seats at 12.00 each with 20 of 31 days left comes to 23.23.

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