The difference is that you submit to the authority the full amount but only 500. At the end of the month will get the interest on the month for 500 euros, annual interest rate of 5%. In the second month you can put another 500 euros when you have 1000 euro + interest over the past month so you get the interest on the 1000 + euros, the rate of 5% again. Personally if I had 6000 fund, for maximum performance without futures, would put me in another account with a high rate and every 14 months would put the 500 in Milennium.