Initial Setting up opening balances

We are already 5 months into our Financial Year and want to migrate to Manager. It is technically not a migration as all our current data is kept on EXCEL.

Our challenge is that by now we have 5 months of Income, Expenses (which involves Accounts Receivables and Payables as well) and we want to use tracking for each revenue and expense for each of our business units.

We are OK to update a cumulated data for 5 months under each GL account separated for each business unit through tracking codes.

Can someone guide us on how do we update initial data in the middle of financial year so it is reflected correctly on Balance Sheet as well.

please read the guides on setting up your chart of accounts and entering starting balances.
https://www.manager.io/guides/9181
https://www.manager.io/guides/15718

Entering all your past transactions is not the usual approach for migration. However, you could use batch operations to do so. I warn you, it will not be easy. See https://www.manager.io/guides/9572.

Read the topic:
Opening Balances for income and expense accounts

In essence you enter the balance of each P&L account in the Journal and balance the Journal by an entry into the Retained Earnings account.

That’s fine for P/L accounts, but what does he do for B/S accounts?

Still uses the normal opening balance sheet balances process.

And what about mvts in B/S for first 5 months?

Movements or transactions are not included when using starting balances. The balance sheet balances are as of the start date. I am fairly sure what @Brucanna was referring to for P&L accounts was a situation where you had already accumulated balances as of the start date, not summarizing transactions since the start date.

To clarify the process.
Let’s say your financial year starts Jan 1, and you are starting with Manager on May 1.
Your Manager start date would be Apr 30. You would enter the balance sheet balances as at the close of Apr 30, including Retained Earnings.
You would also enter via a journal dated Apr 30 the P&L balances as at the close of Apr 30 with the Journal being balanced with a post to Retained Earnings.

This way your May P&L isn’t inflated by the pre May activities.
Also the Retained Earnings account doesn’t get duplicated as Manager in the background posts a complete mirror image of the journal to the Retained Earnings account, not just the
Retained Earnings journal entry, so it has zero effect on the Retained Earnings account.