SaaS · 6 weeks, zero downtime

Migrating live subscription billing with zero failed renewals

Moved a growing SaaS off homegrown invoicing onto Stripe Billing mid-flight: 4,000 active subscriptions migrated, zero failed renewals, involuntary churn cut by more than half.

failed renewals during migration: 0; failed renewals during migration
involuntary churn, down from 4.2%: 1.6%; involuntary churn, down from 4.2%
from first commit to full cutover: 6 wks; from first commit to full cutover

The challenge

Client: B2B SaaS company
Services: Custom Software, SaaS Development
Timeline: 6 weeks, zero downtime

The billing system was a founder-written script that had grown for five years. It worked, mostly, but every pricing change took two weeks of engineering, failed cards silently became churned customers, and finance reconciled invoices in spreadsheets every month end.

The terrifying part was that it was live. 4,000 companies renewed on it every month, and a billing mistake is the one bug B2B customers never forgive.

What we did

The approach, decision by decision

01
Ran both systems in parallel with reconciliation
Mirrored every subscription into Stripe and compared what each system would charge, every day for three weeks, until the diff report came back empty.
02
Migrated in cohorts, safest first
Moved monthly self-serve accounts first, then annuals, then enterprise contracts with custom terms, with instant rollback available at every stage.
03
Turned failed payments into a recovery funnel
Smart retries, card-updater, and a dunning email sequence replaced the silent failures that had been quietly bleeding revenue.

The results

All 4,000 subscriptions migrated with zero failed renewals and zero support tickets about billing.
Involuntary churn dropped from 4.2% to 1.6% within two months of the new dunning flow.
Pricing changes now ship in an afternoon instead of a two-week engineering project.
Finance closes the month from Stripe reports instead of spreadsheets.

Built with

Stripe
Fastify
TypeScript
PostgreSQL
Temporal
AWS

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