Billing and invoicing software source code
Billing and invoicing software sold as source code is a complete invoicing platform — bought once, hosted by you — that issues invoices, chases payment automatically, and in the versions worth buying also runs recurring subscriptions with proration, dunning and tax handling.
Written by ZoopCoder, who build and sell one of the packages described below — that bias is declared in full further down this page.
Quick answers
How much does invoicing software source code cost?
Roughly $40 to $400 for an off-the-shelf licence, against $10,000 to $40,000 for a custom build. The price step is almost entirely recurring billing: an invoice generator is cheap, a subscription engine with proration and dunning is not.
What is the difference between invoicing and subscription billing?
Invoicing issues a document and waits for payment. Subscription billing decides what to charge, every cycle, forever — handling upgrades mid-period, proration, failed cards, retries and cancellations. The second is where almost all the complexity and almost all the revenue leakage lives.
Can self-hosted billing software be compliant?
Yes, if it models tax as rules rather than a single rate. What compliance requires is jurisdiction-specific: sequential invoice numbering, correct tax breakdown per line, the right identifiers on the document, and an immutable record once issued. Check those four before anything else.
The one decision that matters: invoice generator or billing engine
These are sold under the same words and are not the same product. An invoice generator makes a document from line items and emails a PDF. A billing engine owns the subscription: it knows each customer’s plan, computes the charge each cycle including mid-cycle changes, retries failed payments on a schedule, and stops service when the retries run out. If you are billing customers monthly, the generator will fail you in month two.
| Model | What it decides | Best for | Where it breaks |
|---|---|---|---|
| Invoice generator | Nothing — you enter the lines | Agencies and freelancers billing project work | Anything recurring; you end up in a spreadsheet within weeks |
| Billing engine | The amount, every cycle, from plan and usage | SaaS, memberships, hosting, anything subscribed | Proration and mid-cycle plan changes — where cheap scripts silently overcharge |
| Accounting suite | The books, not the billing | Statutory reporting and reconciliation | Weak at automated dunning and customer-facing billing portals |
A quick test on any demo: put a customer on a monthly plan, then upgrade them halfway through the period. A real billing engine issues a prorated credit for the unused part of the old plan and a prorated charge for the new one, and shows both lines on the next invoice. A generator will either charge the full new price immediately or quietly charge nothing until next month.
What a complete billing package must include
These are the pieces that determine whether the software collects money without you watching it. Invoice templates are the part everyone demos; the rest is the part that pays for itself.
- Recurring plans with monthly, annual and custom cycles, plus trials, coupons and one-off add-ons
- Proration on upgrade, downgrade and cancellation — computed, shown as explicit invoice lines, and correct to the day
- Automated dunning: a retry schedule for failed cards, escalating reminder emails, and a defined end state (suspend, downgrade or write off)
- Tax modelled as rules, not a number: per-jurisdiction rates, per-line tax classes, inclusive versus exclusive pricing, and the buyer’s tax identifier on the document
- Sequential, gap-free invoice numbering with per-series control, and invoices that become immutable once issued — corrections happen via credit notes
- Credit notes, partial payments, write-offs and account credit balances
- Multi-currency with the exchange rate recorded on the invoice, not looked up at display time
- A client portal where customers see history, download PDFs, update a card and pay — this alone removes most billing support email
- Gateway integrations that handle the whole lifecycle including webhooks, refunds and card updates, plus manual and bank-transfer payment recording
- An API and webhooks, because billing always ends up connected to something else
What billing software actually costs
The comparison that matters here is not against other scripts — it is against hosted billing platforms that charge a percentage of everything you bill.
| Route | Typical cost | What you get | Time to live |
|---|---|---|---|
| Marketplace script (regular licence) | $39–$89 | Invoice generator with a PDF template; recurring often cosmetic | Days — then the billing engine is yours |
| Open source (Invoice Ninja, Crater, Kill Bill) | Free, or a hosted tier | Strong invoicing; Kill Bill is a genuine billing engine but a large system to run | Days to weeks depending on which |
| Direct vendor, complete platform | $149–$399 | Recurring, proration, dunning, tax rules and client portal included | About a day to deploy |
| Hosted billing platform | 0.5%–0.9% of revenue billed, or $250–$600+/month | Nothing to run; the cost grows with your success | Same week |
The arithmetic that decides this one: a percentage-of-revenue billing platform at 0.5% costs $500 a month once you are billing $100,000 a month, and that is on top of gateway fees. A one-time licence plus a $20 VPS does not move. Against that, self-hosting means you own tax-rule updates, PDF template maintenance and gateway API changes — budget a few engineer-days a year, and more in any year your tax authority changes the rules. Below roughly $20,000 a month billed the hosted option is usually simpler; above it, source code wins on cost and keeps winning.
Where to buy, and what each source is good for
| Source | Best for | Watch out for |
|---|---|---|
| Open source (Invoice Ninja, Crater) | Freelancers and agencies invoicing project work | Recurring billing is basic; proration and dunning are not really there |
| Open source (Kill Bill) | Serious subscription billing you intend to run at scale | A substantial platform with real operational weight — it is infrastructure, not an app you install on shared hosting |
| General code marketplaces | Cheap invoice generators with attractive templates | “Recurring” that means a cron job re-issuing the same amount; no proration, no dunning, no credit notes |
| Direct from the developer | A finished billing platform you can rebrand and resell | Ask to see a mid-cycle upgrade and a failed-payment retry in the demo — both, specifically |
Declared bias: what we sell
We are ZoopCoder. We build and sell CloudBillPro — a billing and invoicing platform with recurring invoices, multi-currency, tax rules, automated dunning, client portal and payment-gateway collection — as source code from $199, with no recurring fee to us. So read this page knowing we are a vendor in the category we just described. Everything above is what we would check if we were buying rather than selling, including the parts that do not favour us: if your requirements are genuinely unusual a custom build beats every package here, and if you want zero operational responsibility a hosted service is simpler than any source code.
If you want a working example to measure against
The CloudBillPro demo runs the full stack, so you can use it as a yardstick for anything else you are evaluating — including the tests described on this page.
If you are comparing against hosted tools
The economics flip based on scale and headcount. These pages lay out the arithmetic against the hosted platforms most buyers weigh up.
Frequently asked questions
What is the best self-hosted invoicing software?
For project invoicing, Invoice Ninja and Crater are the strongest free options and both are genuinely good at issuing and chasing invoices. For subscription billing, the open-source answer is Kill Bill, which is powerful but is infrastructure you operate rather than an app you install. Commercial source code sits between them: less to run than Kill Bill, with the recurring features the free invoicers lack.
Can I bill customers in multiple currencies?
Yes, but insist on one specific behaviour: the exchange rate must be captured on the invoice at issue time and stored, not looked up when the document is displayed. Otherwise an invoice you sent in March shows a different total in June, which breaks reconciliation and, in several jurisdictions, breaks compliance. Ask to see the stored rate field before you buy.
How does automated dunning work?
When a card payment fails, the system retries on a schedule rather than giving up, typically after three, five and seven days, sending the customer an escalating series of emails with a link to update the card. If every retry fails, a defined end state applies: suspend the service, downgrade the plan or write the invoice off. Good dunning recovers a meaningful share of failed payments, which is why it belongs in the software rather than in your inbox.
Is self-hosted billing software GST or VAT compliant?
It can be, and it depends on how tax is modelled rather than on where the software runs. Requirements usually include a correct tax breakdown per line, both parties' tax identifiers on the document, sequential gap-free numbering, and invoices that cannot be edited after issue. Software that stores a single tax percentage per invoice will not satisfy a mixed-rate jurisdiction, so check for per-line tax classes and rule-based rates.
Should I use Stripe Billing or self-host?
It is an arithmetic question. Hosted billing platforms charge a percentage of what you bill, so the cost rises exactly as you succeed, while a one-time licence plus a small server does not. Below roughly $20,000 a month billed, hosted is simpler and cheaper in total effort; above that the percentage starts to fund an engineer. The other factor is control: self-hosting means your customer and revenue data stays in your database.
Can I resell billing software to my own clients?
Only with the right licence, and only if the codebase is multi-tenant. Regular marketplace licences almost always forbid operating the software as a service for other people, and a single-tenant invoicing app cannot isolate one client's customers from another's anyway. If reselling is the plan, confirm both points in writing before paying.
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