Why would a transaction marked "credit" with a positive value deduct from my available balance at the bank?

If your bank hasn’t verified the funds from the entity giving you the credit yet, they won’t make it available for you to access.

That makes sense, but this “credit” has caused my account to overdraft as the amount “credited” has been deducted from my account.

Do you bank with Wells Fargo, by any chance? I had a fight with them over this very issue. I was credited, they didn’t verify the deposit and they withdrew (or withheld) my own preexisting funds to cover it if it was bad.

Call your bank.

Negative. A small regional bank in Tn

Call them. If they’re doing what WF did to me, and caused you an overdraft, it’s bullshit. They’ll have to refund your original funds and wipe out the fees for overdraft. Make sure you get in writing that the overdraft THEY caused is not reported to credit agencies.

Let’s consider a simple example. Say you have $100 on deposit in your checking account. You deposit a check for $10. The bank credits the deposit to your account, showing a new balance of $110. However, since the check has not yet cleared, the “available credit” is reduced by the amount of the deposit, $10.

No money has been “deducted” from your account, but the check is only shown as a provisional credit until it clears. In the case of domestic checks, they should clear within 2–3 days maximum. (In most cases these days the clearing time can actually be measured in hours, but existing laws and bank regulations allow the banks a longer window for clearing, and since the aggregate amounts of money are so high, even for small banks, they take full advantage. Those small amounts, aggregated and left on deposit even at the low short term rates currently available, and even for “just a few days” means a considerable amount to their bottom line at the end of the year.)

As to why your overdraft would have occurred, that should only happen if you wrote your own check for an amount exceeding the $100 you already had on deposit.

Yes @CWOTUS

But what WF did to me was (I don’t remember the exact amount) I had $400 in checking. I received a credit to my account for $312 (it was payroll from a small business).
This happened on a Friday and WF had a policy of guaranteeing unverified credited funds using the depositor’s balance as surety until the deposit cleared – even though the credit is not available to the customer. tricky banking maneuver

They withheld my $312 in this policy (immediately) and I used my debit card over the weekend to the tune of $100. On Monday, they debited the $312 “security” before they processed my legit charges. This caused 4 overdrafts on my debit card, for which they wanted to charge me $45 per incident.