Subscription proration calculator: what is owed after a mid-cycle change? Free, private

What does a customer owe after a mid-cycle upgrade, downgrade or cancellation?

Enter the billing period, the amount already billed and each change with its date. You get the day-count segments, the credit or charge to issue now, tax, the next renewal, and a table of the balance if the same change had happened on other dates. Use it to answer a billing ticket, to check your billing provider's preview, or to set a proration policy.

It works from your own figures. It does not know your billing provider's rounding or your refund terms.

The billing period

What happens to the renewal date

Period start (YYYY-MM-DD)

Renewal date: period end (YYYY-MM-DD)

Amount billed for this period, dollars

Tax on the balance, % (0 if none)

Changes: one per line, the first day the new amount applies, then the new amount per period (0 cancels)

Fill in the period, then click Work out the balance.

Result

Segments

From	To (not included)	Days	Amount per period	Charge

If the first change had happened on another date

Change date	Credit for unused old time	Charge for new	Net balance

What it does, and what it leaves to you

Keep the renewal date: the old amount covers the days before each change and each new amount the days from it, every segment as days / days in the period of that amount, rounded half up to the cent. The balance is the sum of the segments minus what was billed.
Restart the period: credit = billed amount x unused days / days in the period; new charge = the full new amount; the next renewal is one period length after the change date.
Tax is the entered percent of the balance, rounded half up, and is negative for a credit.
Not decided: whether you refund, credit or keep the unused part, your provider's rounding or per-second proration, trials, usage charges, discounts and coupons, tax rules for credit notes, and currencies with other minor units.

Common questions

How do I prorate a subscription upgrade in the middle of a billing period?

Split the period at the change date. The old amount covers the days before it and the new amount the days from it on, each as a share of the period's days. Add the two, subtract what the customer already paid, and the difference is the charge or credit. Paste your dates and amounts and the page does exactly that and shows every line.

Should the renewal date move when someone upgrades?

Both are common. Keeping the renewal date charges only the difference for the days left. Restarting the period on the change date credits the unused old time and bills a full new period from today. The page has a mode for each so you can see what the customer would pay under either.

How is a cancellation or downgrade refund calculated?

Enter the change date and the new amount; 0 means cancelled. The unused days at the old amount come back as a credit. Whether you refund it, keep it as account credit or keep it at all depends on your terms, which this page does not decide.

Does it match Stripe, Chargebee or Paddle?

It uses plain day-count proration rounded half up to the cent. Billing providers can prorate by the second, round differently or apply their own rules, so check the figure against the provider's preview before you rely on it.

Is my billing data uploaded anywhere?

No. The arithmetic runs in your browser and nothing is sent; a test in the code asserts there are no network calls.