Sage 200 uses Accounting Periods to help control how you report on your company's financial position.
Transactions posted into a future accounting period don't post to your nominal accounts, but are held as Deferred until the accounting period is opened.
Deferred transactions post to your customer, supplier and bank accounts, but are not included in the balance of your nominal accounts. This means you can keep up to date with current invoices while you finalise your year end accounts.
When you open the relevant period, the deferred transactions post to the nominal account.
To open accounting periods in a new year, you must first run your Year End.