A Securicor guard helped himself to cash to pay off his debts, a court was told.
Daniel Horn kept two money bags containing more than £35,000 he had collected from customers.
Horn, 22, of Christchurch Road, Worthing, paid more than £10,000 into his bank account the day after the first theft.
Nick Hall, prosecuting, said £5,500 was used to pay off a loan and £4,500 went into his personal account.
Horn kept one of 22 money bags he collected from the Abbey National on January 2 last year. It contained more than £25,000 paid in by customers at the branch in Terminus Road, Eastbourne.
A second bag, containing more than £10,000 collected from Yes Car Credit, of Springfield Road, Horsham, went missing nine days later.
The bags should have been scanned by a hand-held computer and a receipt issued to show that Horn had collected them by armoured van.
Mr Hall told Hove Crown Court: "The prosecution says that Mr Horn saw the opportunity to deliberately miss out one of the bags from the scan, hoping staff would not notice.
"The staff at Abbey National were given a receipt for 21 bags, not 22, so that he could steal that bag containing £25,000. It took a good number of days for these shortages to be noticed. Everyone was assuming a mistake had been made and the takings would turn up somewhere along the line."
He said Horn denied stealing the money, although a conservative estimate of his expenditure was about £25,000, which he got through in the few months following the alleged thefts.
In a statement, Horn said the money had properly been earned, borrowed or given to him as gifts.
Horn denies two charges of theft. The trial continues.
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