FastSpring and Kill Bill both handle recurring billing, but they sit on opposite ends of the build-versus-buy spectrum. FastSpring is a merchant-of-record…
Best for FastSpring: FastSpring fits software and SaaS companies that want to sell globally (200+ regions, 35+ currencies) without taking on VAT and sales tax liability themselves, and that prefer a flat-rate, all-inclusive pricing model over building billing infrastructure.
Best for Kill Bill: Kill Bill fits engineering teams that want to own their billing logic and data outright, are equipped to integrate their own tax engine (via Avalara or Vertex plugins) and payment gateways, and want to avoid the transaction and merchant-of-record fees built into FastSpring's flat-rate model.
At a Glance
FastSpring
Kill Bill
Primary category
Invoicing
Invoicing
Rating
Not documented
Not documented
Pricing model
Custom / Transaction-fee-based (Merchant of Record revenue share)
Open Source (with paid enterprise tier)
Starting price
Custom quote; no published flat rate, commonly cited around 5.9% + $0.95 per transaction depending on volume
Free
Free plan
Not documented
Yes
Free trial
Yes
Not documented
Platforms
Web
Not documented
Team collaboration
Not documented
Not documented
AI features
Not documented
Not documented
Public API
Yes
Yes
Key Differences
Merchant of Record vs. Self-Managed Billing
FastSpring: FastSpring acts as the merchant of record, taking on tax and compliance liability for the seller as part of its service.
Kill Bill: Kill Bill is a billing engine only; it does not act as merchant of record, so the operating company remains responsible for its own tax and compliance obligations, typically via integrated tax engines like Avalara or Vertex.
Merchant-of-record status shifts legal and tax liability to the platform, which removes significant compliance burden but also removes control over the checkout relationship.
Pricing Transparency
FastSpring: FastSpring has no public pricing list; rates are negotiated per business with an account executive using a flat-rate model based on transaction type and volume.
Kill Bill: Kill Bill's core platform is free and open source under Apache 2.0, with no per-transaction or revenue-percentage fees.
Custom-negotiated pricing makes upfront cost comparison harder, while a free open-source core has a knowable direct cost (though not a knowable total cost once engineering time is factored in).
Global Tax and Currency Handling
FastSpring: FastSpring supports 200+ regions and 35+ currencies with automated VAT and sales tax compliance built into the platform, plus 21+ languages.
Kill Bill: Kill Bill connects to third-party tax engines such as Avalara and Vertex rather than handling tax compliance natively.
Native, automated global tax handling reduces implementation complexity for companies selling into many jurisdictions at once.
Fraud Prevention
FastSpring: FastSpring includes built-in risk management and fraud prevention on transactions as part of its service.
Kill Bill: Kill Bill's documented features do not include native fraud prevention; this would need to be handled by the integrated payment gateway or a separate tool.
Built-in fraud tooling reduces chargebacks and fraudulent transactions without requiring a separate vendor integration.
Deployment and Control
FastSpring: FastSpring is a fully managed, hosted checkout and billing platform.
Kill Bill: Kill Bill deploys via Docker or Kubernetes in your own infrastructure, avoiding SaaS lock-in and giving full data ownership.
Infrastructure control affects data residency, customization depth, and vendor lock-in risk.
Feature-by-Feature
Compliance & Risk
Feature
FastSpring
Kill Bill
Merchant of record service
Available
Unavailable
Automated tax compliance (VAT/sales tax)
Available
Limited
Fraud prevention
Available
Not documented
Billing & Payments
Feature
FastSpring
Kill Bill
Subscription/recurring billing management
Available
Available
Multi-currency support
Available
Not documented
Payment gateway plugin architecture
Not documented
Available
Developer APIs
Available
Available
Pricing & Deployment
Feature
FastSpring
Kill Bill
Public pricing list
Unavailable
Available
Self-hosted deployment
Unavailable
Available
Affiliate marketing network
Available
Not documented
Free trial
Limited
Available
Pricing Compared
Starting price reflects the lowest paid tier, not the full cost for every team size or usage level.
FastSpring
Custom (all-in-one transaction fee) — Custom quote, commonly cited around 5.9% + $0.95 per transaction or a flat 8.9% rate depending on volume Per transaction
Merchant-of-record model removes the burden of registering for and filing VAT, GST, and sales tax in dozens of individual countries.
All-in-one flat-rate pricing bundles payment processing, tax, billing, and fraud prevention into a single vendor relationship instead of stitching together several tools.
Long operating history in the digital-goods payments space, dating back to 2005, with established support for global software and SaaS sellers.
Reviewers frequently cite responsive, knowledgeable account management and customer support compared to self-serve competitors.
Cons
No published, self-serve price list; sellers must go through a sales process to receive a custom quote, making upfront cost comparison difficult.
FastSpring keeps its transaction fee even when a sale is refunded, meaning the seller loses both the revenue and the associated processing cost.
Some sellers have reported additional charges, such as a risk assessment fee, that are not reflected on the public pricing page.
As a merchant of record, FastSpring's checkout branding and flow offer less low-level customization than a fully custom integration built directly on a processor like Stripe.
Kill Bill
Pros
Completely free and open source under Apache 2.0
No vendor lock-in and full ownership of billing data
Highly customizable via plugin architecture for gateways, tax, and notifications
Proven at scale in production since 2010
Optional Aviate enterprise layer for teams wanting managed support
Cons
Requires engineering effort to deploy, configure, and maintain self-hosted
No published pricing for the Aviate enterprise tier
Steeper learning curve than hosted SaaS billing competitors like Chargebee or Recurly
Smaller ecosystem and community than some commercial alternatives
Payment gateway and tax integrations depend on plugin maturity
Use Cases
Choose FastSpring: FastSpring fits software and SaaS companies that want to sell globally (200+ regions, 35+ currencies) without taking on VAT and sales tax liability themselves, and that prefer a flat-rate, all-inclusive pricing model over building billing infrastructure.
Choose Kill Bill: Kill Bill fits engineering teams that want to own their billing logic and data outright, are equipped to integrate their own tax engine (via Avalara or Vertex plugins) and payment gateways, and want to avoid the transaction and merchant-of-record fees built into FastSpring's flat-rate model.
Need both: A company scaling internationally could start with FastSpring as merchant of record to launch quickly in new tax jurisdictions, then later migrate core subscription logic to a self-hosted Kill Bill deployment if it decides to bring billing in-house and handle tax and merchant obligations itself.
FastSpring
Global SaaS subscription billing — SaaS companies use FastSpring to sell subscriptions to customers in multiple countries while FastSpring handles VAT, GST, and sales tax collection and remittance in each jurisdiction automatically.
Indie and mid-market software sales — Independent software vendors and mid-market publishers use FastSpring's hosted or embedded checkout to sell desktop software, licenses, and digital downloads without building their own tax and compliance infrastructure.
B2B sales-assisted deals — Enterprise and B2B software sellers use FastSpring's digital invoicing and interactive quoting tools to handle purchase-order and wire-transfer customers alongside self-serve card checkout.
Kill Bill
Custom recurring billing infrastructure — Engineering teams build tailored subscription billing logic without vendor lock-in.
Usage-based and metered billing — Companies with consumption-based pricing models implement custom metered billing workflows.
Multi-tenant white-label billing — Platforms and marketplaces run billing for many tenants or resellers from a single installation.
Frequently Asked Questions
Does Kill Bill act as a merchant of record like FastSpring?
No, Kill Bill is a billing engine only and does not take on merchant-of-record status; FastSpring's core service is acting as merchant of record and taking on tax and compliance liability for sellers.
How is FastSpring priced compared to Kill Bill?
FastSpring uses flat-rate pricing negotiated per business with no public price list, while Kill Bill's core platform is free and open source under Apache 2.0 with no licensing fees.
Does Kill Bill handle VAT and sales tax automatically?
Not natively; Kill Bill connects to third-party tax engines like Avalara and Vertex, while FastSpring handles VAT and sales tax compliance automatically as part of its merchant-of-record service.
How many currencies does FastSpring support?
FastSpring supports 35+ currencies and 200+ regions with localized, branded checkout; Kill Bill's currency handling is not documented in the available facts since it depends on the integrated payment gateway.
Is Kill Bill free to use?
Yes, the core Kill Bill platform is open source under the Apache License 2.0 and free to self-host, though it requires engineering resources to deploy and operate; FastSpring's pricing is custom and requires talking to their sales team.
How large is FastSpring's customer base?
FastSpring reports serving 3,200+ customers and processing over $2 billion in transactions per year; comparable adoption figures are not documented for Kill Bill, though it has been in production for over 15 years since its 2010 founding.