[math] Calculate percentage saved between two numbers?

I have two numbers, the first, is the original price, the second, is the discounted price.

I need to work out what percentage a user saves if they purchase at the second price.

example
25, 10 = 60%  
365, 165 = 55%

What I dont know is the formula to calculate this.

This is function with inverted option

It will return:

• 'change' - string that you can use for css class in your template
• 'result' - plain result
• 'formatted' - formatted result

function getPercentageChange( $oldNumber , $newNumber , $format = true , $invert = false ){

    $value      = $newNumber - $oldNumber;

    $change     = '';
    $sign       = '';

    $result     = 0.00;

    if ( $invert ) {
         if ( $value > 0 ) {
        //  going UP
            $change             = 'up';
            $sign               = '+';
            if ( $oldNumber > 0 ) {
                $result         = ($newNumber / $oldNumber) * 100;
            } else {
                $result     = 100.00;
            }

        }elseif ( $value < 0 ) {        
        //  going DOWN
            $change             = 'down';
            //$value                = abs($value);
            $result             = ($oldNumber / $newNumber) * 100;
            $result             = abs($result);
            $sign               = '-';

        }else {
        //  no changes
        }

    }else{

        if ( $newNumber > $oldNumber ) {

            //  increase
            $change             = 'up';

            if ( $oldNumber > 0 ) {

                $result = ( ( $newNumber / $oldNumber ) - 1 )* 100;

            }else{
                $result = 100.00;
            }

            $sign               = '+';

        }elseif ( $oldNumber > $newNumber ) {

            //  decrease
            $change             = 'down';

            if ( $oldNumber > 0 ) {

                $result = ( ( $newNumber / $oldNumber ) - 1 )* 100;

            } else {
                $result = 100.00;
            }

            $sign               = '-';

        }else{

            //  no change

        }

        $result = abs($result);

    }

    $result_formatted       = number_format($result, 2);

    if ( $invert ) {
        if ( $change == 'up' ) {
            $change = 'down';
        }elseif ( $change == 'down' ) {
            $change = 'up';
        }else{
            //
        }

        if ( $sign == '+' ) {
            $sign = '-';
        }elseif ( $sign == '-' ) {
            $sign = '+';
        }else{
            //
        }
    }
    if ( $format ) {
        $formatted          = '<span class="going '.$change.'">'.$sign.''.$result_formatted.' %</span>';
    } else{
        $formatted          = $result_formatted;
    }

    return array( 'change' => $change , 'result' => $result , 'formatted' => $formatted );
}

The formula would be (original - discounted)/original. i.e. (365-165)/365 = 0.5479...

    function calculatePercentage($oldFigure, $newFigure)
{
    $percentChange = (($oldFigure - $newFigure) / $oldFigure) * 100;
    return round(abs($percentChange));
}

100% - discounted price / full price

I see that this is a very old question, but this is how I calculate the percentage difference between 2 numbers:

(1 - (oldNumber / newNumber)) * 100

So, the percentage difference from 30 to 40 is:

(1 - (30/40)) * 100 = +25% (meaning, increase by 25%)

The percentage difference from 40 to 30 is:

(1 - (40/30)) * 100 = -33.33% (meaning, decrease by 33%)

In php, I use a function like this:

function calculatePercentage($oldFigure, $newFigure) {
        if (($oldFigure != 0) && ($newFigure != 0)) {
            $percentChange = (1 - $oldFigure / $newFigure) * 100;
        }
        else {
            $percentChange = null;
        }
        return $percentChange;
}

I have done the same percentage calculator for one of my app where we need to show the percentage saved if you choose a "Yearly Plan" over the "Monthly Plan". It helps you to save a specific amount of money in the given period. I have used it for the subscriptions.

Monthly paid for a year - 2028 Yearly paid one time - 1699

1699 is a 16.22% decrease of 2028.

Formula: Percentage of decrease = |2028 - 1699|/2028 = 329/2028 = 0.1622 = 16.22%

I hope that helps someone looking for the same kind of implementation.

func calculatePercentage(monthly: Double, yearly: Double) -> Double {
    let totalMonthlyInYear = monthly * 12
    let result = ((totalMonthlyInYear-yearly)/totalMonthlyInYear)*100
    print("percentage is -",result)
    return result.rounded(toPlaces: 0)
}

Usage:

 let savingsPercentage = self.calculatePercentage(monthly: Double( monthlyProduct.price), yearly: Double(annualProduct.price))
 self.btnPlanDiscount.setTitle("Save \(Int(savingsPercentage))%",for: .normal)

The extension usage for rounding up the percentage over the Double:

extension Double {
/// Rounds the double to decimal places value
func rounded(toPlaces places:Int) -> Double {
    let divisor = pow(10.0, Double(places))
    return (self * divisor).rounded() / divisor
   }
}

I have attached the image for understanding the same.

Thanks

If total no is: 200 and getting 50 number

then take percentage of 50 in 200 is:

(50/200)*100 = 25%

((list price - actual price) / (list price)) * 100%

For example:

((25 - 10) / 25) * 100% = 60%