Why you should NEVER bet all-up (multi or parlay) by multiplying the odds on racing or sports betting.

When you multiply the odds on two or more events, you also multiply the percentages against yourself with each event you add.

Take for example the methods used by one or two U.K. bookies. They bet parlay on various soccer matches by multiplying the odds. Each event 
is bet at a percentage of, lets say, 115%. This translates to a takeout of $13 from every $100 invested, so an average of $87 is returned in $100.

Let us say you take a parlay on some soccer matches. Your average return on any event is going to be $87, but we'll say you are a bit smarter than 
some and get an average return of $90 in each $100. So you now have 90% left on the first event, take 10% off the 90%, leaving 81% on a two match 
parlay. Take 8.1% off the 81%, leaving 72.9% on a three match parlay. Take 7.3% off the 72.9%, leaving 65.6% on a four match parlay. Take 6.5% off the 65.6%, leaving 59.1% on a five match parlay. Take 5.9% off the 59.1%, leaving 53.2% on a six match parlay, and on it goes.

115% is low compared to the reality of some soccer books, so we have been conservative with these figures. When you have to bet a four match parlay 
and 10% tax is taken out on top, it is a mathematical fact that usually less than 50% of all the money invested will be returned to the "investors". These 
same figures apply to betting all-up on several races with the totalizator.

If you must bet this way, stick to the doubles, trebles or quadrellas offered on racing, or the fixed odds method of a points spread that U.S. bookies use 
with their sports lines,but that is only marginally better value. The true parlay odds are  2@3/1, 3@7/1, 4@15/1, 5@31/1, 6@63/1, 7@127/1, 8@253/1, 9@511/1, 10@1023/1. Do you think you are getting value for money?

Give yourself a fighting chance - NEVER bet by multiplying the odds.