SaaS Invoicing: Billing Models, Proration, Dunning and Tax

SaaS invoicing is the part of subscription billing that produces the documents: one invoice per billing period per customer, plus extra invoices or credits when something changes mid-period. Getting it right means choosing how each pricing model appears on the invoice, prorating changes the same way every time, retrying failed cards before cancelling, charging the right tax in each place you sell, and keeping invoiced amounts separate from recognised revenue.

This guide is for founders and finance leads at SaaS companies setting up or fixing billing. If you sell a recurring service rather than software (support plans, memberships, retainers), the shorter guide to invoicing subscription services fits better.

What should a SaaS invoice show?

A SaaS invoice needs everything a normal invoice has, plus the information that explains why this period's amount is what it is. The fields below prevent most "why was I charged this?" tickets.

Worked example: one invoice, two service periods. A hybrid plan costs $99 a month including 10,000 API calls, with overage at $0.005 per call. In March the customer made 14,200 calls. The invoice dated 1 April shows:

Without the period column, the customer sees "April" next to a charge for March usage and opens a ticket. Put dates on every line.

How does each pricing model appear on the invoice?

Each pricing model produces a different invoice pattern, and the pattern decides whether you bill in advance, in arrears or both.

Two rules keep usage invoices defensible. Give customers a usage view that matches what the invoice will say, and keep raw usage events long enough to recalculate any period a customer disputes. Stripe's documentation notes that usage-based billing is not subject to proration (Stripe: Prorations), so changes to a metered price simply apply to usage from that point on.

How is proration calculated?

Proration charges or credits the fraction of the period affected by a change: credit the unused time on the old price, charge the remaining time on the new price, and bill the difference. Stripe's own example: upgrading from a $10 to a $20 monthly plan halfway through the month credits $5 and charges $10, so the customer owes an extra $5 (Stripe: Prorations, accessed October 2026).

Worked example: adding seats to an annual plan. A customer pays $360 per seat per year for 12 seats on a 1 January to 31 December term. On 8 August they add 3 seats. From 8 August to 31 December inclusive is 146 of the term's 365 days.

• Charge for new seats: 3 × $360 × 146 ÷ 365 = 3 × $144 = $432.00
• At renewal on 1 January: 15 seats × $360 = $5,400

Three behaviours differ between billing systems and are worth deciding deliberately:

1. When the proration is billed. By default, Stripe adds proration items to the next regular invoice; setting proration_behavior to always_invoice bills the change immediately. For an annual plan, "next invoice" can mean next January, so most teams invoice seat additions immediately.
2. What happens to credits. Stripe states that negative prorations are not automatically refunded. A downgrade credit sits on the account until a future invoice uses it, unless you refund it.
3. Precision. Stripe prorates to the second by default, so its figure for the example above will differ slightly from a day-based calculation. If your contracts say "prorated daily", configure that or calculate it yourself.

A common policy is to prorate upgrades immediately and apply downgrades at the next renewal. Whatever you choose, write it into your terms so the invoice matches what customers agreed to. Credits that reduce an invoice already issued should go on a credit note that references it; see credit notes explained.

Should you charge cards automatically or send invoices?

Use automatic charging for self-serve customers and "send invoice" collection for customers whose finance team pays from their own systems. Most SaaS companies end up running both.

Enterprise buyers usually need the invoice addressed to their legal entity, a purchase order number, your tax forms (a W-9 in the US), and sometimes submission through their supplier portal. Ask for all of it during the sales process, not after the first invoice bounces. The late payment guide covers follow-up on Net-terms invoices.

How should failed card payments be retried?

Retry automatically first, email the customer in parallel, and only restrict or cancel after the retry window ends. This process is called dunning.

Stripe's documentation describes its approach (Stripe: Automate payment retries, accessed October 2026):

• Smart Retries pick retry times using machine-learned signals; the recommended default is 8 tries within 2 weeks, configurable from 1 week to 2 months.
• Hard declines are not retried without a new payment method. Examples include lost_card, stolen_card, incorrect_number and authentication_required.
• After the last retry you choose whether the subscription is cancelled, marked unpaid, left past due, or paused.

Match your emails to that window. With a 2-week retry policy, a workable sequence is: an email on the first failure with a card-update link, a reminder about a week in, and a final notice two or three days before the window closes stating exactly what happens next (read-only access, cancellation). For hard declines, skip straight to asking for a new card, because waiting for retries achieves nothing.

Track recovered revenue and the reasons for failure each month. If one decline code dominates, the fix is usually upstream: card-update prompts before expiry, or offering direct debit to customers on annual plans.

What tax do SaaS invoices need?

Tax depends on where your customer is and how that jurisdiction classifies software, so a SaaS company selling widely usually needs per-customer tax calculation. This section is general information for the US and EU, last reviewed October 2026; it is not tax advice, so confirm your position with a tax adviser or the relevant authority.

United States. States disagree on whether SaaS is taxable. New York, for example, treats prewritten software as taxable whether it is delivered on a disk, by electronic transmission or by remote access (NY Department of Taxation and Finance, TB-ST-128, issued August 5, 2014). Other states exempt SaaS or tax it under a different category. Since South Dakota v. Wayfair (June 21, 2018), states can require out-of-state sellers to collect sales tax without a physical presence; the South Dakota law upheld in that case applied to sellers delivering more than $100,000 of goods or services, or 200 or more transactions, into the state each year (Supreme Court opinion via Cornell LII). Thresholds vary by state. Our sales tax nexus guide explains how nexus works.

European Union. Services sold to businesses in another EU country are usually not charged VAT by the seller; the customer accounts for it under the reverse charge. Electronically supplied services sold to consumers are taxed in the customer's country, with a EUR 10,000 EU-wide threshold for distance sales below which an EU-established seller may apply its home VAT. The One Stop Shop lets you declare that VAT in a single EU country instead of registering in each one (Your Europe: Cross-border VAT, accessed October 2026). Non-EU sellers can use the non-Union OSS scheme for services to EU consumers (European Commission OSS portal).

On the invoice, show the tax rate and amount per jurisdiction, your tax registration number where required, and the customer's VAT number plus reverse-charge wording on EU B2B invoices. The invoice tax compliance guide and VAT invoicing guide cover the content rules.

Why isn't invoiced cash the same as revenue?

Under ASC 606 in the US and IFRS 15 internationally, both introduced in May 2014 (IFRS Foundation: IFRS 15), revenue follows delivery of the service, not the invoice or the payment.

Worked example. A customer prepays $12,000 on 1 January for a 12-month subscription where access is provided evenly over the year. On 1 January the company has $12,000 in cash and $12,000 of deferred revenue (a liability). Each month, $1,000 moves from deferred revenue to recognised revenue. If the customer buys a $3,000 onboarding package on the same invoice, the accountant decides whether it is a separate performance obligation recognised when delivered, or part of the subscription spread over the year.

What this means for invoicing:

• Keep service periods on every line. They are the input to the revenue schedule.
• Separate one-time fees (setup, onboarding, training) from recurring lines.
• Use credit notes, not edits, so the revenue and tax history stays intact.

Early-stage companies often keep cash-basis books, then switch to accrual when raising money or preparing audited statements. The glossary entries on revenue recognition and accrual basis explain the terms.

Which billing stack fits your SaaS?

Choose based on pricing complexity and who you want to handle sales tax.

Sources: Stripe Billing pricing, Paddle pricing, both accessed October 27, 2026.

Worked example: 400 customers at $50 a month ($20,000 monthly), all paying by US card.

• Stripe Billing + Stripe payments: 0.7% × $20,000 = $140; 2.9% × $20,000 = $580; 400 × $0.30 = $120. Total $840 a month (4.2%), before any tax-calculation product and before your cost of registering and filing sales tax or VAT yourself.
• Paddle: 5% × $20,000 = $1,000; 400 × $0.50 = $200. Total $1,200 a month (6.0%), with Paddle acting as the seller and handling tax collection and filing.

The $360 monthly difference ($4,320 a year) is roughly the price of outsourcing global tax compliance and payment disputes. If you sell mainly to US businesses in a few states, it may not be worth it. If you sell to consumers in dozens of countries, it often is. International cards and currency conversion add fees on Stripe, so model your real card mix.

When does an invoicing tool like InvoiceQuickly fit a SaaS company?

InvoiceQuickly is an invoicing tool, not a subscription billing system. It fits a narrow SaaS case: a small number of B2B customers on annual or quarterly contracts who pay by bank transfer or a payment link on Net terms, plus one-off invoices for setup or consulting work.

What it can do for that case, on Pro ($9/month): create invoices by typing or saying what to bill and reviewing the draft; email them with a PDF; add a payment link from your own Stripe or PayPal account for the remaining balance; send scheduled reminders before and after the due date; set up recurring invoices (weekly, monthly, quarterly or yearly) that are created as drafts for review or sent automatically; issue credit notes against an invoice; and record partial payments by bank transfer, card, check, cash or other methods.

Where it does not fit:

• No card-on-file charging, proration, usage metering or automatic retries. Each invoice is paid by the client through a link or by transfer.
• Simple tax only. One tax percentage per invoice, added on top. No per-jurisdiction calculation, and your tax ID is not printed on the PDF (add it to the notes). The recurring-invoice form creates a single line item without tax or discount, so taxed subscription invoices are better duplicated by hand each period.
• No PO field and no accounting connection. Put the PO number in the notes; hand off data with the Pro CSV export, because QuickBooks and Xero are not connected today.

If you have more than a few dozen subscribers or any self-serve sign-up, use processor billing or a merchant of record from the start. The recurring billing guide compares approaches for smaller businesses, and the pricing page lists what each InvoiceQuickly plan includes.

Frequently asked questions

What is SaaS invoicing?

SaaS invoicing is producing an invoice for each subscription billing period and for each change to a subscription, such as an upgrade, a seat change or metered usage. Each invoice shows the service period, plan, quantity, proration lines, discounts and tax, and is either charged automatically to a saved payment method or sent for payment on terms.

Should a SaaS company send invoices or receipts?

Both, depending on the customer. Self-serve customers charged automatically need a paid invoice or receipt for their records. Business customers on Net terms need an invoice before payment, with a due date, their legal entity name and a PO number if they use purchase orders.

How do you invoice usage-based pricing?

Bill usage in arrears for the period just ended, show the metered quantity, the rate and the dates, and give customers a usage dashboard that matches the invoice. On hybrid plans, the same invoice usually carries next period's base fee and last period's overage, so date every line.

Is SaaS subject to sales tax?

It depends on the state or country. Some US states, such as New York, tax remotely accessed prewritten software; others exempt SaaS. In the EU, electronically supplied services to consumers are taxed in the customer's country, while B2B sales usually use the reverse charge. Check each jurisdiction where you have customers, or use a merchant of record.

When should a SaaS company use a merchant of record?

A merchant of record makes sense when you sell to consumers or small businesses in many countries and do not want to register for and file sales tax and VAT in each one. You pay a higher transaction fee (for example 5% + 50¢ at Paddle, as of October 2026) in exchange for the MoR acting as the seller and handling tax.

Do I need a separate billing system if I use Stripe?

Not for most early SaaS companies. Stripe Billing handles subscriptions, invoices, proration and retries on top of Stripe payments. A dedicated billing platform starts to pay off with complex catalogues, several payment processors or detailed revenue schedules.