Differencies between Trial Balance and Account Balance

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Hi!

I have beginner question:
Why there is differences between Trial Balance and Account Balance.

F.ex.
I have a line in trial balance for an bank account for a period of June:
Balance: 529.72, Debit: 619.60, Credit: 1189.22, Balance: -39.90
While when I open a link from account number and get the account transactions table for the same period, then:
the first line (empty one - should be beginning) Balance: 529.72
the last summary line: Debit: 619.60, Credit: 1143.66, Balance: 5.66

The last line is correct one - it is the same like in a bank report.
For next month the beginning balance is not 5.66, but -39.90

So the question is how the beginning balance is calculated?

Thanks in advance,
Janeks