There are differing opinions but a good rule of thumb is 5% but in “crisis periods” that percentage can be three or four times higher.
http://www.lada-xray.net/showthread.php?p=158058#post158058
http://www.prepody.ru/topic49056.html
http://forum3.bandingklub.cz/viewtopic.php?f=14&t=1434852
https://debate.socialism.nl/forum/showthread.php?tid=196403
http://miweii.com/forum.php?mod=viewthread&tid=17505&extra=
https://talk.hyipinvest.net/threads/313203/
https://neoternia.net/viewtopic.php?t=241438
http://ewmen.com/viewtopic.php?t=839732
http://horsecity.ru/phpBB3/viewtopic.php?f=22&t=249014
https://mmomakemoneyonline.net/threads/ditt-og-datt-deler-ogsa-ut-andre-sammenkomst.459696/
http://www.prepody.ru/topic67416.html