Navinder Singh Sarao argued he couldn't put up £5.05m for bail because his assets had been frozen.
The US Justice Department (DoJ) wants him extradited on wire and commodities fraud and market manipulation charges.
The US authorities have said he can be freed if he agrees to come up with the money in the coming weeks.
He also had to say where his money was. The court was told that he had funds of more than £30m, £25.5m of it in Swiss accounts.
Mr Sarao told an earlier hearing at Westminster Magistrates' Court that he had not "done anything wrong apart from being good at my job".
The other bail conditions are that he must stay at his parents' address in Hounslow, west London, each night, and cannot travel internationally or use the internet.
The court was also told that Mr Sarao has been diagnosed with severe Asperger's syndrome.
A full extradition hearing is scheduled for 24-25 September.
The DoJ claims that Mr Sarao and his firm, Nav Sarao Futures, made £26m ($40m) illegally over five years.
He has been accused of using an "automated trading program" to manipulate markets, and of contributing to the flash crash of 6 May 2010. On that day, the Dow Jones index lost 700 points in a matter of minutes - wiping about $800bn off the value of US shares - before recovering just as quickly.
