Short answer
Switching from accounting software to an ERP takes six steps: clean up the old books, design a new chart of accounts with a mapping table, prepare master data, bring opening balances across in detail, cut over on the first day of a financial year or month, and run both systems through at least one month-end close.
Key points
- Never copy the old chart of accounts wholesale; map it and prove the mapping against a real trial balance.
- Receivables, payables, stock and fixed assets must come across item by item, not as totals.
- Cut over mid-month and that month's VAT (PP.30) and withholding returns must combine two systems.
- Keep the old system read-only: Thai law requires accounts and documents to be kept for at least five years.
What are the signs your accounting software is no longer enough?
The clearest sign is a team keying the same data into several places every day, or a new branch that cannot be consolidated into one report. Accounting software keeps the books well; it was not built to hold stock, purchasing and sales for the whole company.
Before you migrate, be clear where the problem actually is. Some businesses do not need a full switch: a stock or sales system that posts into the existing accounting software is enough.
- The same data is keyed into the accounting software, Excel and the sales system every day
- Stock in the system does not match the shelves, or the figures arrive days late
- Each branch or warehouse keeps its own file and someone merges them by hand at month-end
- Management waits for accounting to merge files before seeing cost or profit per product
What do you need to prepare to switch from accounting software to an ERP?
Six things: the chart of accounts, opening balances, master data, open documents, history and the cut-over date. Migrations rarely stall on installation; they stall on legacy data and the cut-over. Sequence the work and daily operations never stop.
The chart of accounts comes first, because an ERP wires it into inventory, purchasing and sales. A chart built for accounting software was usually designed to produce financial statements and nothing else, so lifting it across unchanged tends to leave you unable to split cost by branch or product line.
Cut over on a period boundary, not mid-month, and run the old and new systems in parallel for one cycle before switching the old one off. This is where teams get impatient, and where the trouble shows up at year-end close.
- Chart of accounts. Review it before moving and decide what dimensions to add: cost centres, branches, product lines.
- Opening balances. Every account balance at the cut-over date must reconcile against the old system's trial balance first.
- Master data. Customers, suppliers, and items, with the codes you intend to keep using.
- Open documents. Unclosed purchase orders, sales orders, receivables, and payables move across as open items.
- History. Most of it does not need to migrate. Keeping the old system read-only is usually enough for audit.
- Cut-over date. Pick the first day of a new accounting period and tell everyone in advance when to stop keying into the old system.
- Clean upClear suspense, bank and old receivables in the old system
- New chartDesign the chart with dimensions and map every old account
- Master dataCustomers, suppliers and items, with the codes you will keep
- Opening balancesBring them in detail; they must add up to the old trial balance
- Cut-over dateFirst day of a financial year, or at least of a month
- Parallel runAt least one month-end close, then lock the old system read-only
How Do You Move a Chart of Accounts Into an ERP?
Build a mapping table from every old account to its place in the new chart, then prove the mapping with numbers. Copying the old chart across wholesale is the mistake. Accounting-software charts tend to carry one account per branch or product line, because the software had no other way to split figures. In an ERP those splits belong in dimensions such as branch or cost centre, so the chart keeps only the accounts the financial statements need, and gets a good deal shorter.
Export the old chart and the trial balance for the last closed month. Design the new chart with the dimensions you want, then build the mapping, keeping each old account code in a reference field on the new account so last year's figures can still be traced.
Test it with your own numbers. Run that month's trial balance through the mapping: debits and credits must still balance, and each new account must equal the sum of the old accounts mapped to it. Many old accounts folding into one is harmless. One old account splitting into several accounts or branches needs care, because someone has to allocate the balance by hand and keep the working.
Clean up the old system before any of this. A balance that is already wrong becomes an opening balance nobody can explain, and it is far harder to correct in the new system than in the one that produced it.
- Suspense and clearing accounts. Resolve them to zero rather than carrying an unexplained balance across.
- Bank accounts. Reconcile to the statement up to the latest month.
- Old receivables and payables. Confirm they are genuinely outstanding and correct mistakes in the old system.
- Duplicate customers and suppliers. Merge them to one code each and fill in missing tax IDs, which tax invoices and withholding tax certificates both need.
- Item codes. Retire discontinued items and merge products that exist under more than one code.
- Dormant accounts. Close them in the old chart instead of carrying them into the new one.
Copy the old chart
- Per-branch and per-product accounts come along
- Wrong balances become opening balances
- Nothing proves every figure arrived
Map with dimensions
- Branches and cost centres become dimensions
- The chart keeps only statement accounts
- Old codes sit in a reference field for tracing
- A real trial balance run through the map must agree
What Goes Into Opening Balances, and When Should You Cut Over?
Opening balances are every account's closing balance on the day before cut-over, taken from the old trial balance. Accounts that other modules depend on need their detail, or the new system knows the balance but cannot work with it: it knows what customers owe in total, but cannot match a payment to the invoice it settles.
The best cut-over date is the first day of a new financial year: the whole year's accounts come from one system, and last year's comparatives come from the old one, already closed. If that cannot wait, cut over on the first day of a month at the least. Thai VAT (the PP.30 return) and withholding tax are both filed monthly, so a mid-month cut-over means that month's returns have to be assembled from two systems.
If you are aiming for the start of a financial year, count backwards: an SME-level ERP typically takes around 4–6 months to implement. If the project runs late, moving cut-over to the start of a later month is safer than going live before testing is finished.
- Inventory valuation method. Keep the one you use, whether weighted average or FIFO. If you want to change it during the move, talk to your auditor first: for tax purposes a change needs Revenue Department approval.
- Tax invoice numbering. The new system must not reissue numbers the old one has already used. Agree the new series before day one.
- Stock count. Count as close to cut-over as you can and adjust the old system to match before bringing the figures across.
- Documents that straddle the date. Decide which system owns open items such as purchase orders still awaiting delivery.
| Account | Brought in as | Must agree with |
|---|---|---|
| Trade receivables | Each unpaid invoice, with its due date | Receivables in the old trial balance |
| Trade payables | Each unpaid supplier invoice, with its due date | Payables in the old trial balance |
| Inventory | Quantity and unit cost, per item and per warehouse | The inventory balance in the books, and a physical count close to cut-over |
| Fixed assets | Each asset, with cost, accumulated depreciation and remaining useful life | The old asset register and the trial balance |
| Cash, bank and other accounts | One balance per account | The old trial balance, and bank statements on the same date |
How Long Should the Old System and the ERP Run in Parallel?
At least one month-end close. Running in parallel means keying real transactions into both systems, closing the month in both and comparing the results. If the figures agree within the criteria you set, retire the old system. If not, find the cause and run another cycle.
Parallel running has a real cost: the accounting team does every job twice while it lasts. Agree the pass criteria before you start, which reports get compared and how far apart they may be, and it will not drag on.
Once it passes, set the old system to read-only rather than deleting it, and leave most of the history there. Thailand's Accounting Act requires accounts and supporting documents to be kept for at least five years from the date the accounts are closed, and an old system that still opens answers an auditor's or a Revenue officer's question directly. If it is a subscription you plan to cancel, export the key reports for every month before the contract ends, since access may end with it.
- Trial balance. Every account agrees once run through the mapping.
- Receivables and payables ageing. Each customer's and supplier's outstanding balance agrees.
- Stock quantity and value. Compared per warehouse, and against a physical count.
- VAT reports and the month's withholding tax. Both systems produce the same returns.
- Bank reconciliation. It can be completed entirely from the new system.
- minimum parallel run before retiring the old system
- 1 month-end
- that must agree before the old system goes
- 5 reports
- to keep accounts and documents under the Accounting Act
- 5 years
What should you export from the old accounting software?
Export everything the ERP needs to keep working and everything an auditor may ask to see, before your access to the old system ends. Most accounting software exports reports to Excel or CSV, but vendors differ, and some reports only come out as PDF, which you can keep and read but cannot import.
Do a real test export during planning and check the files carry their codes: customer codes, item codes, document reference numbers. Without them, matching records on import becomes manual work that takes far longer than most people expect. If the old product is a subscription, ask the vendor in writing how long you can still view or export data after you stop renewing.
- Chart of accounts and the trial balance for the last closed month
- Customers and suppliers, with tax IDs and the addresses used on tax invoices
- Items with codes, units and unit cost, per warehouse
- Each outstanding customer and supplier invoice, with its due date
- Fixed-asset register: cost, accumulated depreciation and remaining life
- Input VAT, output VAT and withholding tax reports for every month you must keep
- The full-year general ledger, saved as files for audit questions
What makes an accounting system migration fail?
People and data, rather than software. Any mainstream ERP handles basic accounting. What differs is how well the company prepares its data, agrees its criteria and frees up its team's time.
- No owner on the accounting side, so IT or the vendor decides the chart of accounts instead of the people who close the books
- Balances that are already wrong get carried across and must be chased in a system with none of the old history
- Going live mid-month to hit a deadline, so that month's PP.30 return combines two systems
- No agreed pass criteria for the parallel run, so it drags on until the accounting team is exhausted
- Training users after go-live instead of having them key real documents before cut-over
- Customising every screen to look like the old program, losing the ERP's benefits and making upgrades hard
Do you have to replace everything?
No. When the problem sits in one area, such as stock, multi-channel sales or job costing, keeping the accounting software for the books and adding a system for that one area, which posts its figures into accounting, is often faster and lower-risk than moving the whole company onto an ERP.
This works when the accounting team is happy with its software and the sticking point is a process specific to your company that an off-the-shelf ERP would need customising for anyway. Agree up front which system owns which number, or the double keying comes back.
Checklist before cut-over
- Are suspense accounts cleared and bank accounts reconciled up to the latest month?
- Has the chart-of-accounts mapping been tested against a real trial balance?
- Do the detailed receivables, payables, stock and fixed-asset balances add up to the trial balance?
- Is cut-over on the first day of a month or financial year, and does everyone know when to stop keying into the old system?
- Is the new tax invoice number series agreed, with no overlap?
- Are the parallel-run pass criteria written down?
- Have the reports you must keep for five years been exported before access to the old system ends?
Frequently asked questions
How do you migrate a chart of accounts into an ERP?
Build a mapping table showing where each old account lands in the new chart, adding dimensions such as cost centres, branches or product lines, because the ERP uses that chart to post entries automatically whenever stock is received or sold. Then run the last closed month's trial balance through the mapping; it must agree before you bring in balances at the cut-over date.
Can you switch to an ERP mid-year?
Yes, but it makes that year's close messier, because the figures have to be combined from two systems. If you have the choice, cutting over on the first day of a new accounting period is far simpler. If a mid-year switch is unavoidable, bring balances in at the cut-over date and keep the old system read-only until that year's accounts are closed.
How long does switching from accounting software to an ERP take?
For an SME-level ERP, typically around 4–6 months from scoping to go-live, plus at least one month-end close running the old and new systems side by side. What usually delays it is legacy data that needs cleaning first: suspense balances nobody can explain, receivables that do not reconcile, duplicate item codes. Installing the system is rarely the slow part.
Which opening balances have to go into an ERP?
Every account's balance at the cut-over date, taken from the old trial balance, plus the detail behind the accounts other modules depend on: each unpaid customer and supplier invoice, inventory as quantity and unit cost per warehouse, and fixed assets one by one with their accumulated depreciation. Each group's detail has to add up to its trial balance figure before the first new transaction is keyed.
How long do we need to keep the old accounting software after switching?
Keep the data for at least five years from the date the accounts are closed, which is what Thailand's Accounting Act requires for accounts and supporting documents. The simplest way is to leave the old system read-only rather than migrating all the history into the ERP. If it is a subscription you are cancelling, export the trial balance, general ledger and tax reports for every month before the contract ends.
Do we have to migrate all our history into the ERP?
No. Migrate what the ERP needs to keep working: the chart of accounts, opening balances, master data and open documents. Keep the transaction history in the old system, read-only, or as exported files. If reports need last year as a comparative, load monthly balances per account rather than every transaction.