Field notes
Amendments are where home-built true-ups break
Building the monthly arithmetic is easy. Keeping it right through an upgrade, a downgrade or a renegotiated commit is where every setup we heard about falls back to manual work.
About these field notes. They draw on public discussions with RevOps, billing and NetSuite practitioners in October 2026, in which several people described how their teams run usage true-ups today. We paraphrase and don't name anyone. The worked examples are illustrations we built to show the mechanics, not any company's real figures.
Three setups, one weak spot
We heard from teams running true-ups three different ways: a scheduled job on Stripe with a database table, a custom record and script in NetSuite, and an iPaaS recipe into a billing system with an Excel check before close. Each described the routine months as handled. What they said about the rest:
- On Stripe, amendments were "a manual adjustment half the time".
- In NetSuite, the team closes the old commitment record and opens a new one with the new terms. It works, but history, rollover and the audit trail end up split across two records.
- With the iPaaS setup, someone still spot-checks the drawdown in a spreadsheet before every close.
Two of the three named amendments outright as the unsolved part. An engineer who has built this logic for several SaaS companies put the fix plainly: start a new segment from the amendment date, and never rerun from the start of the contract.
The rule: new segment, never rerun
Treat a contract as a series of segments. Each segment has its own terms and runs from one date to the next. An amendment doesn't edit the contract's history; it ends the current segment and starts a new one.
- Close the current segment on the amendment's effective date. If that falls mid-period, the partial period is settled on the old terms, with included units prorated if the contract says so.
- Carry the balance forward. Unexpired rolled credits move into the new segment and keep their original expiry dates. They don't get a fresh clock because the plan changed.
- Apply the new terms only from the effective date. Periods already invoiced stay as invoiced.
- If something earlier was wrong, post an adjustment on the next open invoice instead of rewriting the old one. See append-only ledgers.
An upgrade in month 7
A 12-month contract includes 10,000 units a month, overage at $0.50. The customer uses 12,000 a month and is invoiced $1,000 of overage in each of months 1 to 6. In month 7 they upgrade to 15,000 a month, overage at $0.40.
| New segment from month 7 | Rerun from month 1 | |
|---|---|---|
| Months 1–6 | Unchanged: $6,000 invoiced, correct when sent | Recomputed on a 15,000 allowance: zero overage |
| Months 7–12 | Zero overage on the new terms | Zero overage |
| Result | Invoices match what was agreed | Credits against $6,000 of correct invoices |
A rerun is easy to trigger by accident: change the allowance cell at the top of the sheet and every earlier month recalculates.
Questions to settle for every amendment
| Question | Common default |
|---|---|
| Effective from when? | The amendment's effective date, or the next period start if the contract says so |
| Is the interrupted period prorated? | Included units prorated by days |
| What happens to unused included units in the interrupted period? | Carried forward, expiring when that period would have ended, or forfeited. Decide which. |
| Do rolled credits keep their expiry? | Yes |
| Is the rollover cap now based on the new commit? | Usually yes, from the next full period |
| Which overage rate applies to the interrupted period? | The old rate |
None of these defaults is universal. The point is to choose, write it in the amendment, and apply it the same way each time.
Why it matters beyond the invoice
- Disputes: a customer who upgraded expects the new terms from the effective date, no earlier and no later.
- Revenue recognition: rewriting closed periods means rewriting what was already recognized.
- Audit and diligence: "why did this invoice change?" needs an answer months later.
Have amendments in your book?
We model each amendment as its own segment and show where invoices diverge from the contract, period by period. Free, within 48 hours of complete files.