Hey, you're flipping currencies! Next buy price PC / ( #S x ( 1 + SAFE + Minimum Trade Size ) ) = 30 / ( 1 x 1.2 ) (assuming 10% safe, 10% min trade size) = £25 next buy price Next Sell Price PC / ( #S x ( 1 - SAFE - Min Trade size ) ) = 30 / ( 1 x 0.8 ) = $37.50