As online marketers, we have to deal with numbers a lot. To identify lucrative ads, to calculate conversion rate changes, or to evaluate the ad spend per customer.

And yes, it happens to most of us: We don’t have all the formulas and calculations ready in our brains at any time.

That’s why I gathered the most important formulas here. So you can shine with stellar knowledge in percentage calculation. Even if you are having one of these blockhead days.

You are welcome.

## Conversion rate formulas

### Calculate conversion rate

Formula: goal completions / visitors x 100 = conversion rate
Example: 50 form submits / 500 visitors x 100 = 10% conversion rate

Please note that Google Analytics calculates conversion rates with number of sessions, not number of users.

Conversion rate = %

### Calculate change in conversion rate

Formula: ( new conversion rate / old conversion rate - 1 ) x 100 = conversion rate change
Example: ( new conversion rate 9 / old conversion rate 7 - 1 ) x 100 = 28.57% conversion rate change

Calculate your change in conversion rate:

Change in conversion rate = %
Conversion rate multiplied by: x

## Performance & finance formulas

### Calculate cost per actioncost per lead (CPL), cost per order (CPO),cost per click (CPC), cost per acquisition (CPA), etc.

Formula: marketing or ad spend / actions = cost per action
Example: \$5000 marketing spend / 132 orders = \$37.88 cost per order

Cost per action = \$
Can be any currency, obviously.

### Calculate return on advertising spend (ROAS)

Example: ( \$1,100 revenue from ads - \$1,000 ad spend ) / \$1,000 ad spend * 100 = 10% return on advertising spend

Return on advertising spend (ROAS) = %

### Calculate return on investment (ROI)

Formula: ( revenue - investment ) / investment * 100 = return on investment in %
Example: ( \$10000 revenue - \$5000 invested capital ) / \$5000 invested capital * 100 = 100% return on investment

Calculate your return on investment (ROI):

Return on investment (ROI) = %

### Calculate change in revenue

Formula: ( revenue in period b or ab test variation / revenue in period a or ab test control - 1 ) x 100 = revenue change
Example: ( \$12000 revenue in period b / \$10000 revenue in period a - 1 ) x 100 = 20% revenue change

Change in revenue = %
Revenue multiplied by: x

## Bounce & engagement formulas

### Calculate bounce rate

Formula: visits without engagement / total visits * 100 = bounce rate
Example: 120 visits without engagement / 360 total visits * 100 = 33.33% bounce rate

Bounce rate = %

### Calculate change in bounce rate

Formula: ( new bounce rate / old bounce rate - 1 ) x 100 = bounce rate change
Example: ( new bounce rate 7 / old bounce rate 14 - 1 ) x 100 = -50% bounce rate change

Calculate your change in bounce rate:

Change in bounce rate = %
Bounce rate multiplied by: x

### Calculate engagement rate

Formula: visits with engagement / total visits * 100 = engagement rate
Example: 1500 visits with engagement / 10000 total visits * 100 = 15% engagement rate

Engagement rate = %

### Calculate change in engagement rate

Formula: ( new engagement rate / old engagement rate - 1 ) x 100 = engagement rate change
Example: ( new engagement rate 50 / old engagement rate 40 - 1 ) x 100 = 25% engagement rate change

Calculate your change in engagement rate:

Change in engagement rate = %
Engagement rate multiplied by: x

## Growth marketing formulas

### Calculate product virality

Product virality is a complex topic. The calculator below suggests that you have a product where customers can invite other people to use the product, too.

Formula: number of customer base x ( number of invitations each customer shares x conversion rate of each invitation ) = number of new customers
Example: cusomter base of 4000 x ( 15 invitations per customer x 5% invitation conversion rate ) = 3000 new customers

New customers:
Viral coefficient:

The viral coefficient has to be 1 or higher to achieve true virality. With a viral coefficient >1, your product will spread and generate more and more new customers continuously while you sip your Espresso Martinis. Oh, and: Yes, that’s hard.

### Calculate customer retention rate

Formula: ( customers at end of period - customers acquired in period ) / customers at start of period x 100 = retention rate
Example: ( 210 customers on January 31st - 10 customers acquired in January ) / 205 customers on January 1st x 100 = 97.56% retention rate