An account can end a day at the same balance and be charged one overdraft fee or four. The difference comes from the order in which the day's transactions are settled.

Authorisation and settlement are separate events

When a card is tapped, the merchant asks the bank whether funds exist and places a hold. Money does not move at that moment.

Settlement happens later, usually overnight, when the bank processes the day's items together as a batch.

Because the account is only truly updated at settlement, the running balance a customer sees during the day is an estimate, not a record.

Sequence inside the batch changes the fee count

A fee is charged per item that settles against insufficient funds, not per day. So the number of items that fall below zero is what determines the total.

Take a day with three small purchases and one large one. Settle the small ones first and only the large item overdraws the account, producing one fee.

Settle the large one first and it drains the balance, so all three small items overdraw, producing three fees on identical spending.

High-to-low ordering was once standard

Processing the largest item first was widely used and was defended on the grounds that important payments, such as rent or a mortgage, should clear before minor ones.

It also happened to maximise fee counts, which drew sustained litigation and regulatory attention in the United States.

Many institutions have since moved to chronological posting or to grouping credits before debits, and several have removed or capped the fee altogether under competitive pressure.

Pending holds distort the picture further

Some merchants place a hold larger than the eventual charge. Fuel pumps and hotels do this routinely, because the final amount is unknown at authorisation.

That hold reduces the available balance for a period, so a later transaction can overdraw against money that will never actually be spent.

The hold is released afterwards, but the fee triggered while it sat there is already recorded.

What actually reduces exposure

The practical defence is to stop relying on the displayed balance and to know which items are still pending. A few habits do most of the work:

  • Check the available balance rather than the current balance, since only one accounts for holds.
  • Ask the bank whether it posts chronologically, and what its per-day fee cap is.
  • Decline the optional debit card overdraft coverage if declined transactions are preferable to fees.

The fee is a function of process, and the process is disclosed in the account agreement rather than in the app.