Â£150 minus commission of winnings. In effect you have backed a 1/2 shot.
Yes until you go on Betfair and get used to the figures, you can just reverse the odds to win to find out the odds to lose: so if you’re laying a 4/1 shot, you’re backing it at 1/4 to lose (which should make you think twice about it!).
For this reason, I rarely lay horses at under 3/1. The feeling that you get from laying a horse at, say, 6/1 and it winning (so you’ve lost Â£400 from trying to win Â£60) is pretty galling.
I always back at level stakes (each bet is ‘one point’), and always lay with a liability of one point. I work out the maximum stake which will amount to that.