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SaaS Proration Calculator

Work out exactly what a mid-cycle plan change costs. Enter the billing cycle, the effective date, and both full-cycle prices to see the unused credit, the remaining charge, and the net amount due or refunded — with every assumption visible and both day-count conventions side by side. No signup required.
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This calculator is powered by Founderpath — built to help founders access capital faster, deploy it smarter, and stay in control of their cash flow.

How it works

3 steps · Instant results
  1. 01
    Pick the kind of changeAn upgrade, a downgrade, a cancellation, or a new customer starting partway through a cycle — each one credits and charges differently.
  2. 02
    Enter the cycle dates and full-cycle pricesCycle start, renewal date, and the day the change takes effect, plus what each plan costs for a complete month or year — then set the day-count and rounding conventions your billing terms use.
  3. 03
    Get the credit, the charge, and the workingAn invoice-style breakdown with both day-count conventions side by side, the full formula you can paste into a support reply, and a CSV export. Nothing is stored and no signup is required.
The calculator
Free · No email · Runs in your browser

Customer moves to a more expensive plan mid-cycle — credit the old plan, charge the new one.

The billing cycle

When the current period runs, and when the change lands

Billing cadence

The plans

Full-cycle list prices, before any proration

Currency

Display only — no conversion is applied

Conventions

The assumptions that make two correct answers differ

Day-count method
Is the effective day billed on the new plan?
Rounding

The adjustment

What the customer is credited, charged, and owes right now

Amount due now
$109.68
Charge on the next invoice
Unused time on previous plan17 of 31 days credited back
−$54.29
Remaining time on new plan17 of 31 days charged
$163.97
Net due$109.68
This billing cycle
14 days used (2026-01-01)17 days prorated (2026-02-01)
Old plan daily rate
$3.19
New plan daily rate
$9.65
Unused credit
$54.29
Remaining charge
$163.97
The full working
Old daily rate = 99 ÷ 31 = 3.1935
New daily rate = 299 ÷ 31 = 9.6452
Unused credit = 3.1935 × 17 days = 54.29
Remaining charge = 9.6452 × 17 days = 163.97
Net = 163.97 − 54.29 = 109.68

Key Insights

  • Once this change renews at full price, recurring revenue moves by $200.00 a month. Proration only settles this cycle — net revenue retention is where the change actually shows up.
  • The same change is $3.65 different under the other day-count convention ($109.68 on actual calendar days vs $113.33 on the fixed 30-day basis). Neither is wrong — but your invoice and your customer's spreadsheet need to use the same one.
  • This is a cash adjustment, not revenue recognition. The credit and charge settle the invoice; the revenue is still earned across the days it covers. Keep the two apart in your chart of accounts.

Actual calendar vs fixed 30-day

The same plan change under both conventions

 Actual daysFixed 30-day
Divisor31 days30 days
Unused credit$54.29$56.10
Remaining charge$163.97$169.43
Net$109.68$113.33

Stripe, Chargebee, Recurly, and Maxio each apply their own timestamp, tax, coupon, trial, and rounding rules on top of this. Treat the number above as the defensible arithmetic, not a guaranteed match to your processor's invoice.

More upgrades than downgrades? That is fundable revenue.

Expansion revenue from existing customers is the strongest signal a revenue-based lender underwrites. Get capital against it without giving up equity.

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The guide

How to Calculate SaaS Proration

The Proration Formula

Net due = (New plan daily rate × Days remaining) − (Old plan daily rate × Days remaining)Daily rate = Full-cycle price ÷ Days in cycle

Proration is two calculations that happen to net against each other. The customer has already paid for days they will not use on the old plan, so those days come back as a credit. They will use the rest of the cycle on the new plan, so those days are charged at the new rate. The difference is what appears on the invoice — a charge on an upgrade, a credit or refund on a downgrade or cancellation.

Worked example: a customer on a $99/month plan upgrades to $299/month on 15 January, in a cycle running 1 January to 1 February. That cycle is 31 days, and 17 days remain from the 15th onward. The old daily rate is $99 ÷ 31 = $3.1935, so the unused credit is $54.29. The new daily rate is $299 ÷ 31 = $9.6452, so the remaining charge is $163.97. The customer owes $109.68 now, and $299 from 1 February onward.

Reverse the same change — $299 down to $99 — and the arithmetic is identical but the sign flips: a $109.68 credit. Whether that credit is refunded in cash or held against the next invoice is a policy decision, not a maths one, and it is worth writing into your terms before a customer asks.

The Two Assumptions That Change the Answer

Day-count convention — actual calendar days or a fixed cycle

Dividing by the real length of the cycle means the daily rate changes between a 28-day February and a 31-day January. Dividing by a fixed 30 days (or 365 for annual plans) keeps the daily rate constant but stops it reconciling exactly to the full-cycle price. Both are defensible; using one on the invoice and the other in the spreadsheet is what starts the argument.

Whether the effective day is billed on the new plan

Charging the change day at the new rate is the common default. Leaving it on the old plan shifts one day of revenue and is nearly invisible on a monthly plan — but on an annual plan a single day can be tens of dollars, and it is exactly the kind of discrepancy a finance team will query.

Rounding

Rounding the credit and the charge separately, rather than rounding the net, can leave a cent of difference against your processor. That is harmless once and a reconciliation problem across thousands of invoices. Pick one rule and apply it everywhere.

Monthly vs Annual Proration

Monthly proration is small and self-correcting: the worst case is a few days of a single month's price, and the next renewal resets everything. Annual proration is where real money moves. A customer upgrading eight months into a $12,000 annual contract carries a credit worth roughly $4,000 and a charge worth whatever the new tier costs for those four months — an adjustment large enough that it belongs in your cash forecast rather than your support queue.

Mid-cycle starts are the other common annual case. Signing a customer partway through a cycle so their renewal aligns with the rest of your book means charging only the remaining days now, then the full price at renewal. It makes the first invoice look small, which is a support conversation worth getting ahead of, and it makes month-one MRR look lower than the contract actually implies.

Proration Is Not Revenue Recognition

The single most common mistake is treating the prorated charge as the revenue for the period. It is not. Proration settles cash on an invoice; revenue is still earned across the days the service is delivered, and under ASC 606 an annual upgrade recognizes over the remaining term rather than in the month the invoice lands. If you are booking these adjustments straight to revenue, your monthly numbers will be lumpy in a way your growth is not — set up the deferred-revenue treatment properly in your SaaS chart of accounts first.

The metric that should move is recurring revenue at the new run rate, not the one-off adjustment. An upgrade is expansion MRR, a downgrade is contraction MRR, and a cancellation is churn — all of which land in net revenue retention and churn rate, not in the prorated invoice line. Roll the new run rate into ARR only from the renewal, not from the change date.

Common Proration Mistakes

Crediting the full cycle instead of the unused days

Refunding the whole month on an upgrade hands back revenue for days the customer already used. It feels generous in the moment and quietly costs a few points of margin across a year of upgrades.

Prorating discounted plans off list price

If the customer pays a negotiated rate, both the credit and the charge must use that rate. Mixing list price into one side of the calculation is the single most common source of a disputed invoice.

Forgetting tax, coupons, and usage overages

Proration applies to the subscription line. Tax is recalculated on the adjusted amount, percentage coupons follow the plan, and metered usage is billed separately in arrears — which is why a processor invoice can differ from a hand calculation even when both are right.

Letting downgrades take effect immediately

Most SaaS companies apply upgrades immediately and downgrades at the next renewal. Applying both immediately means issuing refunds for service the customer keeps using until the end of the period.

What Plan Changes Say About Your Financing Options

Individual prorations are small. The pattern behind them is not. A book where mid-cycle upgrades outnumber downgrades is a business with expansion revenue and net revenue retention above 100% — the single strongest signal a revenue-based lender underwrites, because it means existing customers grow the revenue that repays the advance without any new sales.

That matters for how you fund growth. Recurring revenue with demonstrable expansion supports non-dilutive financing at a known cost, repaid from the revenue itself. Founderpath funds bootstrapped SaaS companies from $10K MRR — no equity, no board seats. Model the alternative with the Equity Dilution Calculator and check how long your current cash lasts with the Runway Calculator.

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Proration settles one invoice. These calculators tell you what the plan change did to the business.

Financial Health

Beyond the calculator

Mid-cycle upgrades are expansion revenue. Expansion revenue is collateral.

Founderpath turns proven recurring revenue into capital — without dilution.

One proration is an invoice line. A pattern of upgrades outrunning downgrades is net revenue retention above 100% — existing customers growing your revenue without any new sales. That is exactly what a revenue-based lender underwrites, and it is why a bootstrapped SaaS company can raise against its billing data instead of a pitch deck.

Try Founderpath Free
  • Borrow against recurring revenue, not projectionsConnect your billing data and the expansion, contraction, and churn behind these plan changes becomes the underwriting file. No forecast to defend, no board deck to build.
  • Keep the equity your retention just earnedNet revenue retention above 100% is the hardest thing in SaaS to build. Selling equity to fund growth hands away a permanent share of it; revenue-based financing costs a known amount and ends when it is repaid.
  • Repay from revenue as it arrivesPayments flex with what you collect, so a month of heavier downgrades does not turn into a missed fixed payment.
  • Know the total cost up frontEvery offer states the total fees before you accept, so you can compare the real cost of capital against what the growth it funds is worth.
  • Close in 24–48 hoursConnect your billing and banking data and get a funding offer within 48 hours — no pitch decks, no term sheet negotiations, no months of diligence.
Questions
10 answers

Frequently asked questions

Proration is the adjustment that settles a subscription when a customer changes plans partway through a billing cycle. It has two halves: a credit for the days of the old plan the customer paid for but will not use, and a charge for the days of the new plan they will use before the next renewal. The net of the two is what lands on the invoice.
Net due = (New daily rate × Days remaining) − (Old daily rate × Days remaining)

Each daily rate is the full-cycle price divided by the days in the cycle. Example: on a 1 January – 1 February cycle (31 days), a customer upgrading from $99 to $299 on 15 January has 17 days remaining. The credit is $99 ÷ 31 × 18 = $54.29 and the charge is $299 ÷ 31 × 17 = $163.97, so $109.68 is due now and $299 from the next renewal.
Both are used in practice. Actual calendar days reconciles exactly to the full-cycle price but gives a different daily rate in February than in January. A fixed 30-day (or 365-day) basis keeps the daily rate constant and is easier to explain, but will not divide evenly into a 31-day month. Pick one, state it in your billing terms, and make sure your invoice and your finance model use the same one — this calculator shows both side by side so you can see the size of the gap.
Identically — the cycle is just longer, so the amounts are much larger. A customer eight months into a $12,000 annual plan has roughly $4,000 of unused credit, and the charge for the new tier covers only the remaining four months. Because the numbers are material, annual prorations belong in your cash forecast rather than being treated as a support-desk detail, and the day-count convention you choose can move the answer by tens of dollars.
That is a policy question, not a maths one. The calculator gives you the unused portion; whether you refund it in cash, hold it as account credit, or let service run to the end of the paid period is set by your terms. Most SaaS companies let the subscription run to the end of the cycle and issue no refund, which is why the cancellation date and the service-end date are often different.
Billing platforms layer their own rules on top of the same arithmetic: proration to the second rather than the day, tax recalculated on the adjusted amount, coupons and trials applied in a particular order, metered usage billed separately in arrears, and their own rounding. This calculator gives you the defensible base arithmetic and shows every assumption, so you can find which rule explains the difference — it does not promise an exact match to Stripe, Chargebee, Recurly, or Maxio.
No. Proration settles cash on an invoice; revenue is still earned across the days the service is delivered. Under ASC 606 an annual upgrade recognizes over the remaining term rather than in the month the invoice lands. Booking the adjustment straight to revenue makes monthly numbers lumpy in a way the underlying growth is not — set up deferred revenue properly in your chart of accounts instead.
The prorated adjustment does not change MRR — the new run rate does, and only from the renewal onward. An upgrade is expansion MRR, a downgrade is contraction MRR, and a cancellation is churn. Those flow into net revenue retention and churn rate, which is where a plan-change pattern actually shows up. Roll the new rate into ARR from the renewal date, not the change date.
A book where mid-cycle upgrades outnumber downgrades means net revenue retention above 100% — existing customers growing your revenue without new sales, which is the strongest signal a revenue-based lender underwrites. Founderpath provides non-dilutive financing to bootstrapped SaaS founders from $10K MRR, repaid from revenue — no equity, no board seats. Compare it against raising with the Equity Dilution Calculator.
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