Less aggressive compilation with CSS3 calc

Less no longer evaluates expression inside calc by default since v3.00.

---

Original answer (Less v1.x...2.x):

Do this:

body { width: calc(~"100% - 250px - 1.5em"); }

In Less 1.4.0 we will have a strictMaths option which requires all Less calculations to be within brackets, so the calc will work "out-of-the-box". This is an option since it is a major breaking change. Early betas of 1.4.0 had this option on by default. The release version has it off by default.

A very common usecase of calc is take 100% width and adding some margin around the element.

One can do so with:

@someMarginVariable = 15px;

margin: @someMarginVariable;
width: calc(~"100% - "@someMarginVariable*2);
width: -moz-calc(~"100% - "@someMarginVariable*2);
width: -webkit-calc(~"100% - "@someMarginVariable*2);

There is several escaping options with same result:

body { width: ~"calc(100% - 250px - 1.5em)"; }
body { width: calc(~"100% - 250px - 1.5em"); }
body { width: calc(100% ~"-" 250px ~"-" 1.5em); }