Why you can't trust your online bank balance

There's only one way to know how much money you have left

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If you rely on your online bank balance to tell you how much money you have left to spend, be warned; this accounting slip-up could push your finances off course.

Last Friday I lost my Santander bank card. as well as be annoying and inconvenient I was worried that the card may have been used by someone quite easily because it is contactless and purchases of up to £20 can be made without a pin or signature.

I thought I'd left it in the Tesco I had been to earlier in the day, where I had spent £12.99, so called the bank and cancelled my card. Unfortunately, the lady on the phone couldn't see an updated list of transactions so asked me to check online on Monday and call back if any payments were amiss.

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I check on the Monday and found two other payments, both to Tesco, of £13.04 and £15.00. I called Santander to explain the situation to them and find out when these transactions had been made. All the while I was worried that further rogue transactions were yet to appear.

After a long and drawn out process of bouncing to different departments I was finally put in touch with a very nice man called Darryl who seems to be the only one in Santander HQ who can tell you when transactions on your account were made – and whether they were made after I lost my card.

The strange thing was, the two Tesco transactions that appeared on my account on Friday night had been made 'at some point in the past six months', by me.

I know what you're thinking because I thought the same: how can transactions made so long ago they can't even give me the correct date be showing now. How come the money was only just taken from my account now?

Darryl explained that this is a hitch in retailers' systems.

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When you purchase an item, the money is deducted from the amount available to spend in your account straightaway but it is not typically deducted from your actual balance – ie. the amount in your bank account – until a couple of days after.

This is a standard timeframe for processing payments.

What had happened in my case is that Tesco did not take the payments of £13.04 and £15.00 in the usual two day window and the money I had spent became available in my account again.

This doesn't mean that Tesco had forgotten I owed them this money, they just took it months later, 'probably when they processed a batch of receipts', said Darryl.

Thankfully there was money in my account to cover the payments but I asked Darryl what would have happened if my account had tipped into an unauthorised overdraft. The short answer is, I would have been charged.

For those living on a tight budget, if you're a stickler for knowing what's going in and out of your account, or just don't want to see your bank account tipped into the red, relying on your online bank balance to tell you how much you have to spend isn't a good idea.

Going old school

I've taken a leaf out of my nan's book to make sure I'm not taken by surprise by a payment again. She used to make a visit to the building society with her passbook when she needed money and wouldn't make a note of what she had spent.

I've now set up an app on my phone that lets me record incomings and outgoings, separated into various categories so that I can see exactly what I've spent and, more importantly, give me the correct figure when it comes to how much I have left.

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