Starting a finance app should not make you appear to earn every pound, dollar or dirham you already own. An opening balance describes your starting position. It is not income generated during the period you are about to track.
This is a small setup decision with a long afterlife. Get it wrong and every later report can look plausible while telling the wrong story.
Choose one clear starting date
Suppose your tracking begins immediately after September 30. At that point, your current account holds 4,000, savings hold 6,000 and a credit card liability is 1,500. Your opening net position across those balances is 8,500.
The 10,000 of cash is not October income. The card liability is not October spending. They are balances carried into the new tracking period.
Use statements or other dated evidence for the same cutoff wherever possible. Mixing a current-account balance from September 30 with a card balance from October 5 can omit or duplicate activity between those dates.
Make the import boundary match the balance date
A common mistake is entering the balance shown on October 5 and then importing transactions from October 1 onward. Those transactions may already be reflected in the October 5 balance.
Choose either an earlier opening balance followed by all later transactions, or a later opening balance followed only by activity after that cutoff. Do not combine the two approaches without a deliberate reconciliation.
Where statements show pending activity separately, establish whether the opening figure includes it. The same pending item should not later be added again as though it were new.
Bring liabilities and other assets into the picture
Opening cash alone can make the starting position look healthier than it is. Include relevant debts and other assets within the reporting scope, with their ownership and dates.
For a holding, the quantity and valuation date matter. For a property, distinguish an estimated asset value from the associated debt. For a joint asset, record the ownership basis instead of assuming that the entire value belongs to one person.
You do not need perfect historical detail to start. You do need to distinguish a documented balance from an estimate and to identify missing information honestly.
Keep corrections out of ordinary income
If a starting balance later proves wrong, record the correction in a way that preserves its purpose. A missing 200 from the opening position should not become a mysterious salary payment in the current month.
Retain the evidence for the corrected amount, the date changed and the reason. That makes a later review far easier than reconstructing why the first month contained unusual income or spending.
Before adding years of history, test a short period. Calculate opening balance plus inflows minus outflows and compare the result with the closing statement. A successful small reconciliation is worth more than a large import that merely finishes without an error message.