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.
How It Works
1
Pick the kind of change
An upgrade, a downgrade, a cancellation, or a new customer starting partway through a cycle — each one credits and charges differently.
2
Enter the cycle dates and full-cycle prices
Cycle 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
Get the credit, the charge, and the working
An 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 billing cycle
When the current period runs, and when the change lands
Billing cadence
Cycle Start
Renewal Date
Change Effective Date
The plans
Full-cycle list prices, before any proration
Current Plan Price, Full Cycle ($)
New Plan Price, Full Cycle ($)
Currency
Display only — no conversion is appliedConventions
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
$109.68Unused time on previous plan
17 of 31 days credited back−$54.29
Remaining time on new plan
17 of 31 days charged$163.97
Net due
$109.68
This billing cycle
$3.19
$9.65
$54.29
$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 days | Fixed 30-day | |
|---|---|---|
| Divisor | 31 days | 30 days |
| Unused credit | $54.29 | $56.10 |
| Remaining charge | $163.97 | $169.43 |
| Net | $109.68 | $113.33 |
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.
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.
Related SaaS Calculators
Proration settles one invoice. These calculators tell you what the plan change did to the business.
Financial Health
Profit and Loss Statement Template — Build a P&L and export it to Excel, Google Sheets or PDF
SaaS Chart of Accounts Template — Generate a SaaS-specific chart of accounts and export it to Excel or Google Sheets
Burn Rate Calculator — Calculate net burn rate, cash runway, and burn multiple
ARR Calculator — Calculate annual recurring revenue from monthly subscriptions and annual contracts
MRR Calculator — Break down new, expansion, contraction, and churned MRR
Churn Rate Calculator — Measure customer and revenue churn with annualized projections
NRR Calculator — Track net revenue retention and gross revenue retention rates
SaaS Quick Ratio Calculator — Measure growth efficiency — MRR gained for every dollar lost to churn
Growth Rate Calculator — Calculate MoM, YoY, and CAGR growth rates from revenue data
Break-Even Calculator — Find the units and revenue needed to cover all costs and reach profitability
EBITDA Margin Calculator — Calculate EBITDA margin and benchmark against SaaS and industry norms
SaaS Runway Calculator — See how many months of cash you have left and model scenarios to extend it
SaaS Financial Model Template — Forecast MRR, ARR, burn, and runway over 24 months with scenario comparison and CSV export
SaaS ROI Calculator — Decide whether a hire, campaign, or tool returns more than it costs
SaaS Debt Capacity Calculator — See how much debt your recurring revenue can safely carry, and what limits it
Customer Metrics
CAC Calculator — Measure customer acquisition cost and LTV:CAC ratio
LTV Calculator — Calculate customer lifetime value, lifespan, and LTV:CAC ratio
Payback Period Calculator — Calculate how long it takes to recover customer acquisition costs
Viral Coefficient Calculator — Measure your K-factor and model viral growth scenarios
SaaS Magic Number Calculator — Measure sales efficiency — net-new ARR per dollar of S&M spend
Pricing & Valuation
Markup Calculator — Calculate markup percentage, selling price, profit, and gross margin
Equity Dilution Calculator — Model how funding rounds affect founder ownership over time
SaaS Valuation Calculator — Estimate your company value using ARR multiples and growth-rate benchmarks
Revenue Multiple Calculator — See what ARR multiple your growth rate, NRR, and gross margin justify
Rule of 40 Calculator — Score your growth-plus-profitability against the Rule of 40 benchmark
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.
Connect 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.
Net 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.
Payments flex with what you collect, so a month of heavier downgrades does not turn into a missed fixed payment.
Every 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.
Connect your billing and banking data and get a funding offer within 48 hours — no pitch decks, no term sheet negotiations, no months of diligence.
Frequently Asked Questions
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.
© 2026 Founderpath, Inc. All Rights Reserved.
