"We are talking, according to the Swiss central bank, about some 30 billion ($38 billion)," Reynders told Belgian public radio RTBF.
Reynders had been in Switzerland earlier this week, and the former finance minister added that "if we tax this at more than 30 percent, we are talking about 10 billion or so that could come back to Belgium".
The minister says Switzerland, which has already brokered deals to tackle tax evasion with Germany and London, and is also in talks at present with Greece and others, has offered to sign an agreement that would see a forfeit on deposits held by Belgian nationals.
Dutch-language daily De Morgen said on Thursday that this would run to a one-off 34 percent of funds worth €30-35 billion, and thereafter a 25
percent annual levy on earnings arising from the assets.
Previously, no figures had been put on Belgian deposits.
However, Belgian politicians are divided on the issue, some arguing that this would leave tax-dodgers getting off lightly.
The Swiss deal with Germany has come under fire from German state tax authorities who have alleged that Swiss banks are aiding German clients to evade tax by routing funds through their branches in such centres as Hong Kong, China and Singapore.