SaaS billing platform decisions are tactical until they hit scale; then they’re strategic. The counterintuitive claim: for many B2B products the buyer-vendor default (Stripe + a billing SaaS) is higher-risk on margins and differentiation than a targeted in-house build once you cross predictable volume and complexity thresholds.
Direct answer: buy when your billing is standard recurring subscriptions and your team's time is better spent on product. Payments plus a billing layer can be live in weeks, and published fees are modest at low volume: Stripe charges 2.9% + 30¢ per domestic card payment and Stripe Billing adds 0.7% of billing volume on pay-as-you-go (Stripe pricing). Consider building, or a hybrid, only when you need billing logic vendors handle poorly (nested usage metering, custom enterprise invoicing, marketplace payouts) and when your projected three-year vendor fees clearly exceed the cost of the engineers who would build and run it. Price both sides with your own revenue and team numbers, not rules of thumb.
The stakes are dollars and time. On fees: Stripe's standard US card fee is 2.9% + 30¢ per transaction (Stripe pricing), while a merchant of record such as Paddle charges 5% + 50¢ per transaction but also takes on sales tax and VAT handling (Paddle pricing), so compare what each fee covers, not just the rate. Every percentage point of take rate is easy to translate: 1% of $3M in annual revenue is $30,000 a year. On people: the U.S. Bureau of Labor Statistics puts the median annual wage for software developers at $135,980 (May 2025) (BLS), before benefits and overhead, so even a three-engineer team costs over $400,000 a year in salary alone. Those two numbers decide whether building ever makes financial sense.
Beyond pure fees there are operational costs: PCI scope, chargeback handling, tax and VAT automation, invoice templates for enterprise contracts, dunning sophistication, and revenue recognition. SaaS vendors cover most of this but at a price and with limited policy control; in-house solutions give control at the cost of engineering time and ongoing maintenance.
SaaS billing platform: vendor vs. in-house tradeoffs
Cost math is simple to model. Example A, buy (illustrative, using published list prices): on $100,000 a month in card revenue, Stripe's 2.9% comes to about $2,900 a month plus 30¢ per payment, and Stripe Billing's 0.7% adds $700 a month (Stripe pricing). Recurly's Starter plan is listed at $249 a month plus 0.9% of billing volume, with the first $40,000 of monthly billings included (Recurly pricing). Example B, build: three engineers at the BLS median wage cost about $408,000 a year in salary before benefits (BLS), plus infrastructure, compliance work and ongoing maintenance. Note that a build still pays card processing fees; it only removes the billing layer's fee. At most volumes, year one favors buying, and building only wins if the billing-layer fees you avoid, plus revenue a custom system unlocks, exceed the team's cost over your planning horizon.
Use-case complexity matters more than raw revenue. If you offer nested metering (per-customer subaccounts with independent quotas), multi-entity revenue recognition, or real-time credit allocation for marketplace payouts, engineering scope multiplies, and so does integration work per enterprise customer. Vendors that support these workflows often reserve them for enterprise plans with quoted, unpublished pricing, so get a written quote at your projected volume before you compare.
Operational risk is underpriced by buyers. Disputes cost more than the fee: Stripe charges $15 for each dispute received (Stripe pricing), and the larger costs are the lost revenue and the staff time to gather evidence and respond. Vendors automate part of this but keep you in a standardized flow. Building gives you policy control, such as custom dispute triage and retry logic, but someone has to own payments operations, and that headcount belongs in your cost model.
Treat billing as a product decision: buy to accelerate market fit; build when fees, product differentiation, or regulatory control exceed an explicit dollar threshold.
How to calculate the three-year TCO and build decision
Step one: quantify your effective vendor take rate. Combine payment processing (Stripe lists 2.9% + 30¢ per US card payment), the billing layer (Stripe Billing lists 0.7% of billing volume; Recurly Starter lists $249 a month plus 0.9%) (Stripe pricing, Recurly pricing), and any merchant-of-record or add-on fees. Then translate one percentage point into dollars on your own revenue: 1% of $200,000 a year is $2,000; 1% of $3M is $30,000. Put the result into a three-year net present value calculation at your own cost of capital.
Step two: add build and run costs. A minimal in-house billing stack needs backend engineers, someone owning infrastructure and reliability, and someone owning payments operations. Price them at fully loaded cost, which is well above the BLS median wage of $135,980 for software developers (BLS) once benefits and overhead are included. Add cloud costs for the database, ledger storage, background workers and egress, and budget ongoing maintenance every year after launch: billing code changes whenever pricing, tax rules or payment methods do.
Step three: include switching and opportunity costs. Migrating customers off a vendor means moving payment methods, subscription state and invoice history, and it usually needs customer success time as well as engineering. Estimate it as a project in engineer-weeks at your own loaded cost. Also count the opportunity cost: the same engineers could ship core product features that improve retention, so estimate what that is worth in revenue before committing them to billing.
