How to double ecommerce revenue: the arithmetic.

What does it actually take to go from $400,000 a month to $800,000?

Most answers start with a channel, a budget, or a new agency. I would start somewhere less exciting. A doubling target is a sum, and the sum has to work before any of those choices matter.

When you write it out, most doubling plans fail on paper. Not because the ambition is wrong, but because the plan quietly assumes the next customer costs what the last one did. It never does.

Revenue is two businesses added together

Monthly revenue has two parts that behave very differently. Returning-customer revenue is what people who have already bought from you spend this month. New-customer revenue is the number of first-time buyers multiplied by what they spend on that first order.

Written as a formula: revenue = returning revenue + (new customers × first-order AOV). Shopify’s own Customers reports give you most of the inputs. The new vs returning customers report shows the split, and the customer cohort analysis shows how quickly each month’s new customers come back.

The two halves move at different speeds. Returning revenue is the output of customers you acquired in the past. It grows as the customer base grows, and the base grows slowly compared with a target that doubles inside a year. You cannot budget returning revenue up this quarter. Almost all of the doubling has to come from the other half.

A worked example: $400,000 to $800,000 a month

Here is an illustrative brand. This is arithmetic, not a client result, and the inputs are round on purpose so you can swap in your own. Today it makes $400,000 a month: $160,000 from returning customers and $240,000 from 3,000 new customers at an $80 first order. It spends $90,000 a month on ads, and to keep the sum simple we treat all of it as acquisition spend. Contribution margin, after cost of goods, shipping, payment fees, and returns, is 45% of revenue.

The target is $800,000 a month. Over the same period, returning revenue grows from $160,000 to $200,000, because the brand is acquiring more customers than it loses. The table shows what the target requires at two assumptions about the cost of the extra customers, plus a third column where the brand also works on first-order value and margin.

Three things stand out. First, doubling revenue needs 2.5 times the new customers, not twice as many, because returning revenue only grew by a quarter. Second, in both middle columns revenue doubles and profit falls. At a $60 marginal CAC, the brand does twice the business for no contribution at all. Third, the last column is the only version where doubling revenue also grows profit, and it gets there by needing fewer customers and earning more on each order, not by buying them more cheaply.

Why the 3,001st customer costs more than the 3,000th

The ad platforms tell you this themselves, if you read the bidding documentation closely. Google’s guidance on Target ROAS says that if you want more conversion volume, you should consider gradually lowering the target, which lets the bid strategy enter more auctions. Those extra auctions are the ones it previously judged not worth the price. More volume is bought by accepting worse value per dollar.

Meta works on the same principle with different mechanics. More budget means reaching people further from your best buyers: less familiar with the brand, less ready to buy, more expensive to convert. The first customers you acquire are the easiest ones. Every step up the budget reaches a slightly harder audience.

This is why average CAC is the wrong number for a growth plan. Say the brand lifts spend from $90,000 to $108,000 and new customers rise from 3,000 to 3,400. Average CAC moves from $30 to $31.76, which looks almost unchanged. But the extra $18,000 bought 400 customers, which is $45 each. That $45 is the marginal CAC, and it is the price of growth. The average blends it with the cheap customers you already had and hides it.

The decision rule: a $40 ceiling in this example

Here is the rule I would use before approving any doubling plan. Work out the most you can pay for each extra customer before the extra revenue stops paying for itself.

If margin stays the same, the ceiling is simple: contribution margin rate × revenue added ÷ new customers added. In the example, that is 45% × $400,000 ÷ 4,500 = $40. Below $40, doubling adds profit. Between $40 and $60, revenue doubles and profit shrinks. Above $60, contribution after ads turns negative: the brand is paying to grow.

1. Set the target and the month you want to hit it.
2. Project returning revenue for that month from your cohort history, not from hope. If your last twelve months of returning revenue grew 25%, use something close to that.
3. Subtract projected returning revenue from the target, divide by first-order AOV, and you have the new customers the target needs.
4. Subtract today’s new customers. That is the number you have to buy at the margin.
5. Compute the ceiling: contribution margin rate × revenue added ÷ extra new customers.
6. Measure your actual marginal CAC with a spend step test, and compare the two.

One honest caveat. This is a first-order view. A new customer who comes back three times is worth more than their first order, and a brand with strong repeat behavior can afford to pay above the in-month ceiling. That is a real choice, but it is a cash choice, not a free one. The CAC payback calculator turns it into months, and months are what your bank balance feels.

Three levers that move the ceiling when the sum fails

If your measured marginal CAC sits above the ceiling, more budget will not fix the plan. The work moves from the ad account to the business. There are three levers, and the table’s last column shows two of them.

• →First-order AOV. Lifting it from $80 to $92, through bundles or a better threshold for free shipping, cuts the new customers needed from 7,500 to 6,522. Almost a thousand fewer customers to buy at the most expensive end of the curve.
• →Contribution margin. Moving from 45% to 48% applies to every dollar of revenue, old and new. In the last column, the ceiling that holds today’s $90,000 of profit rises from $40 to about $58, so a $45 marginal CAC now clears it comfortably.
• →Retention. If returning revenue reached $260,000 instead of $200,000, the target would need 6,750 new customers instead of 7,500. Retention work is slow, which is exactly why it has to start before the growth push rather than after it.

None of these is a media tactic. That is the point. A doubling plan that only has a media answer is usually a plan to buy revenue at a loss.

What common advice gets wrong: double the budget, double the revenue

The most common version of a growth plan I see is a spreadsheet where ad spend doubles and revenue doubles alongside it, at the same MER. It is comforting because it turns growth into a budget request. It is wrong because it treats spend as a multiplier when it behaves like an input with diminishing returns.

Run it through the example. Doubling spend to $180,000 at a $45 marginal CAC buys 2,000 more new customers, for 5,000 in total. That is $400,000 of new-customer revenue. Returning revenue has had less time to grow, say to $175,000. The month lands at $575,000: revenue up 44% on a budget up 100%. MER falls from 4.44 to 3.19, and contribution after ads falls from $90,000 to $78,750.

The brand spent twice as much and made less money. Nothing went wrong in the ad account. The plan simply asked the account to do something the curve does not allow.

When this arithmetic is wrong

The model assumes a rising cost curve and a slow-growing returning base. There are situations where either assumption breaks, and you should know which one you are in before trusting the sum.

• →Your best campaigns are capped by budget, not by their targets. When an efficient campaign runs out of money every day, the next dollars can cost close to what the last ones did, for a while. Marginal CAC is flat until the headroom runs out.
• →The growth comes from somewhere new: a new market, a new product line, or a new channel. Each has its own curve, and its first customers are cheap again. The ceiling still applies, but you measure it per curve.
• →Your customers reorder quickly. Replenishment and subscription brands grow returning revenue much faster than a once-a-year purchase. Model it from monthly cohorts rather than a single growth rate.
• →You measure during peak season. A step test in November tells you what customers cost in November. Run it in a normal month, or read it against the same weeks last year.
• →A large share of revenue sells outside your store, through wholesale or a marketplace. Store revenue then understates what ads produce, and the returning half of the formula is not all in Shopify.

What to do this month

1. Pull the last three full months from Shopify: returning-customer revenue, new customers, and first-order AOV. Use the customer cohort analysis to see how returning revenue has grown over the past year.
2. Write down the target and the month. Compute the new customers required and the extra ones you have to buy.
3. Compute your ceiling from contribution margin, not gross margin. If you do not know your contribution margin, stop here and work it out first. Every other number in this plan depends on it.
4. Run a step test before November: raise acquisition spend about 20% for two to three weeks, and divide the extra spend by the extra new customers against a matched prior period. That is your marginal CAC. If you cannot finish it by mid-October, run it in January and read it against the same weeks last year.
5. If marginal CAC is below the ceiling, the budget is the plan. If it is above, the plan is AOV, margin, or retention, and the budget waits.

The ecommerce growth milestone planner does this sum for any revenue target: new customers, spend, MER, and cash. For how the answer changes at each stage of growth, the guide to scaling an ecommerce business walks the whole ladder, and the new-customer half of the formula is only as good as your definition of new, which is the subject of what a new customer really costs.

If you would like a second pair of eyes on your version of this sum, the free audit reads your ad account and shows where spend is going without return, which is where I would look first before signing off any doubling plan. It is where I would begin before signing off any doubling plan, including my own.