Rounding up or down when 0.5

manpreet Best Answer 2 years ago

I am having an issue with the way Javascript is rounding numbers when hitting 0.5. I am writing levies calculators, and am noticing a 0.1c discrepancy in the results.

The problem is that the result for them is 21480.705 which my application translates into 21480.71, whereas the tariff says 21480.70.

This is what I am seeing with Javascript:

(21480.105).toFixed(2)
"21480.10"
(21480.205).toFixed(2)
"21480.21"
(21480.305).toFixed(2)
"21480.31"
(21480.405).toFixed(2)
"21480.40"
(21480.505).toFixed(2)
"21480.51"
(21480.605).toFixed(2)
"21480.60"
(21480.705).toFixed(2)
"21480.71"
(21480.805).toFixed(2)
"21480.81"
(21480.905).toFixed(2)
"21480.90"

Questions:

• What the hell is going on with this erratic rouding?
• What's the quickest easiest way to get a "rounded up" result (when hitting 0.5)?

manpreet 2 years ago

This seems to do the trick.

The rounding problem can be avoided by using numbers">numbers represented in exponential notation:

function round(value, decimals) {
  return Number(Math.round(value+'e'+decimals)+'e-'+decimals);
}

console.log(round(21480.105, 2).toFixed(2));