Trial balance, every account
Total debits, total credits, and closing balance per account compared between your system and the shadow ledger. Not a sample — every account, every night.
Migration · methodology
Every migration page on this site repeats the same rule, so it deserves its own explanation. We do not retire your existing system until a shadow ledger has tied to its trial balance across three consecutive closed months — not a spot check, not one clean month, three full closes where the numbers agreed without anyone intervening.
Connect your current system read-only and watch it reconcile. Stop at any point having lost nothing.
184 consecutive days tied · variance $0.00
Every night, both directions. A difference raises an exception with the underlying transactions attached rather than being absorbed.
What is actually checked
A migration that only compares closing balances can be wrong in several ways that produce a matching total. These are the checks that catch those.
Total debits, total credits, and closing balance per account compared between your system and the shadow ledger. Not a sample — every account, every night.
AR, AP, inventory, and fixed assets each tie to their control account independently. A trial balance can agree while a subledger underneath it does not.
Counts by type and period alongside value totals, because two errors of equal size in opposite directions produce a matching balance and a wrong ledger.
The shadow ledger must reproduce what your books looked like on a past date, not just what they look like now. That is what tests the history rather than the current state.
Opening balance, movement, closing balance per account per period. A rollforward that ties is meaningfully stronger evidence than a closing balance that does.
Any difference produces an alert with the transactions attached. Nothing is written off to a rounding account and nothing is plugged.
A month counts toward the three only once it is closed in your existing system. An open period that agrees proves considerably less.
A single month can agree by construction. If the shadow ledger was built by copying balances rather than by reprocessing transactions, the first comparison is a tautology — you have compared a number to itself and learned nothing.
Three consecutive closed months forces the shadow ledger to handle a full cycle of real events: accruals reversing, prepaids amortising, intercompany matching, revenue schedules advancing, and at least one period-end adjustment somebody posted late. Those are where migrations are actually wrong.
Three is a compromise. Twelve months would test annual events — the audit adjustment, the bonus accrual, the year-end revaluation — and nobody would run a parallel system for a year to find out.
Three catches the monthly cycle reliably and misses genuinely annual behaviour. We say that plainly rather than implying the rule is exhaustive, and where a customer has unusual quarterly events we extend rather than pretending three covers it.
A month counts only once it is closed in your existing system. An open period agreeing proves much less, because the entries that most often diverge — accruals, reclassifications, and late adjustments — arrive during the close rather than during the month.
In practice this means the three months are three closes, which for a team closing in fourteen days is a longer calendar period than the number suggests. That is understood when we plan it.
It frequently does not, at first. The differences we find fall into four categories and each is handled differently.
On several engagements the three-month clock has restarted twice, pushing a planned cutover by a quarter. That is an uncomfortable conversation and it is a better one than the alternative, which is discovering the problem after the old system has been retired and the evidence is gone.
Revenue timing, mostly. A migration that could nominally complete in six weeks takes four to five months to reach retirement, and we cannot recognise it as complete until it is. It also means occasionally telling a customer their data has problems we did not create.
We think it is the right trade. Every finance system migration is a bet that the new numbers are right, and the three-month rule is the only mechanism we have found that settles the bet before the evidence is destroyed.
Questions
Connect your current system, let the shadow ledger reconcile nightly, and decide about migrating later.