[DeadMilkman]

Update: I found the problem with my original formula, I'm an idiot as usual, and missplaced a (.

So I have runs some tests, and all 4 of the methods discussed work as they should.
Method 1. using 40 - ( Int(([%Level%] - 1) / 7) * 10)
Method 2. using 40 - ( Trunc(([%Level%] - 1) / 7) * 10)
Method 3. using 40 - ( Round(([%Level%] - 1) / 7) * 10)
Method 4. using 40 - iif([%Level%] >= 19, 30, iif([%Level%] >= 15, 20, iif([%Level%] >= 8, 10, 0)))

Each method gives slightly different results as expected, except that Trunc and Int seem to be the same.

Hopefully this will be usefull to everyone.