Unit Economics Every Founder Should Track

Every other metric depends on how much each unit contributes after its direct costs, so get this number right first.

Two margins are often confused:

• Gross margin subtracts cost of goods sold: for software, typically hosting, payment processing and support tied to delivering the service.
• Contribution margin subtracts all costs that vary with each sale, which can also include sales commissions, transaction fees and marketing that scales with revenue.

Golden Egg Check, a startup investment platform, gives a worked example in which a company with a healthy gross margin has a much lower contribution margin once commissions and performance marketing are counted. It warns that misclassifying variable costs as overhead makes growth look more profitable than it is (Golden Egg Check).

Contribution margin per unit = revenue per unit - variable costs per unit
Contribution margin %        = contribution margin / revenue

Write down which costs you count as variable and keep that list fixed from month to month. RaiseMoney notes that some costs change behavior with scale, such as hosting that is mostly fixed at low volume and variable later, so document the treatment and apply it consistently (RaiseMoney).

Customer acquisition cost (CAC) is what you spend to win one customer. The basic formula, as Kruze puts it, is total sales and marketing expense divided by the number of customers acquired in the period (Kruze Consulting).

The common mistake is counting only ad spend. The LTV-CAC Book guide lists what a fully loaded CAC includes: marketing salaries, sales commissions, ad spend, software tools, agency fees, content production, events and an overhead allocation (LTV-CAC Book). Founders should include a fair estimate of their own time if they are doing the selling. Otherwise CAC will look close to zero until the day you hire a salesperson.

Three rules keep CAC honest:

1. Keep two numbers, clearly labeled. RaiseMoney suggests tracking a paid-media CAC for daily campaign decisions alongside a fully loaded CAC, and never presenting the smaller one as the total (RaiseMoney).
2. Match spend to the sales cycle. If deals take months to close, dividing this month's spend by this month's customers compares unrelated groups. Use a rolling period.
3. Split by channel. A blended CAC averages a cheap channel with an expensive one and describes neither. RaiseMoney gives an example where referrals and paid campaigns produce very different costs per customer, and the blended average hides that (RaiseMoney).

Lifetime value (LTV) estimates how much margin a customer produces over the whole relationship. A common subscription shortcut, given by Kruze, is:

LTV = (average revenue per account x gross margin %) / churn rate

(Kruze Consulting)

Two adjustments make it more honest.

Use margin, not revenue. The LTV-CAC Book calls this critical: lifetime revenue overstates value because it ignores the cost of serving the customer (LTV-CAC Book). Contribution margin is stricter still and is the better choice if you have large variable costs beyond hosting.

Prefer observed retention to a formula. The shortcut assumes churn is stable forever. RaiseMoney notes that it becomes unreliable when cohorts are young, churn changes over time, expansion revenue is material or a few large customers distort the average. It suggests reporting both the observed figure and the model, for example "six-month observed contribution per customer is X; modelled lifetime contribution is Y based on current churn" (RaiseMoney).

The bank Mercury makes the same point from the other side: LTV relies on forecasts, so it is best assessed by cohort and segment, with care taken that large outliers do not skew it (Mercury).

The LTV to CAC ratio. Dividing LTV by CAC shows how much value each acquisition dollar returns. Kruze's guide, read on 2026-10-17, describes 3:1 or higher as a common benchmark (Kruze Consulting). Treat any benchmark as a prompt for questions rather than a target. RaiseMoney points out that a very high ratio may mean you are underinvesting in growth, not that your engine is ideal (RaiseMoney).

CAC payback is the number of months it takes for a customer's margin to repay what you spent to acquire them.

CAC payback (months) = CAC / monthly margin per customer

The SaaS CFO, a finance blog by a fractional CFO, defines it as the months required to pay back upfront acquisition cost after the variable cost of serving the customer, and describes CAC as a kind of debt: you pay it upfront and earn it back in monthly installments (The SaaS CFO).

That framing explains why payback matters so much to young companies. If you push growth with long payback, the business needs more and more capital to grow. The same source adds two caveats. The formula ignores churn, so a customer who leaves before payback leaves an unpaid balance that the next customers must cover. And it ignores the time value of money, so long paybacks are worse than they look.

Stripe's guide summarizes the difference between the two most cited metrics: LTV to CAC measures the overall return on acquiring a customer, while payback measures how quickly that cost is recovered (Stripe). An early company can have an attractive lifetime ratio and still run out of cash because the money comes back too slowly.

Retention is the input that moves every other number. Mercury notes that even small increases in churn can dramatically shrink LTV and weaken the LTV to CAC ratio, and that improving retention is often one of the most powerful levers available (Mercury).

Track three views:

• Logo retention: the share of customers from a starting cohort still paying after one, three, six and twelve months.
• Revenue churn: the revenue lost each month to cancellations and downgrades.
• Net revenue retention (NRR): revenue this period from a cohort of existing customers, including upgrades, divided by that cohort's revenue at the start.

Baremetrics explains that NRR captures cancellations, downgrades and expansion together. Above 100 percent means revenue from existing customers grows even after churn, and when expansion outweighs churn you reach "negative churn" (Baremetrics).

The most useful chart is a cohort retention curve. The LTV-CAC Book calls monthly cohort curves that flatten, rather than keep declining, the most powerful evidence that LTV projections are grounded in real data (LTV-CAC Book).

Put the metrics on one sheet and review them on the same day each month.

An illustrative example. A subscription product charges a customer an average of 100 per month, pays 20 per month in hosting, payment fees and support, and loses 4 percent of customers each month. Fully loaded CAC is 600.

Monthly margin per customer = 100 - 20 = 80
Modeled LTV                 = 80 / 0.04 = 2,000
LTV to CAC                  = 2,000 / 600 = about 3.3
CAC payback                 = 600 / 80 = 7.5 months

Then split by channel. If referral customers cost 150 to acquire and paid search customers cost 1,400, the paid search payback is well over a year even though the blended number looks fine. That is a decision, not a statistic: cut paid search, fix its conversion or raise prices for that segment.

Watch for the distortions that make unit economics look better than they are:

• Discounts left out of revenue. Use the price customers actually pay after discounts and credits, not list price.
• Annual prepayments counted as monthly margin. Cash collected upfront helps runway, but margin per month is still the annual amount divided by twelve.
• Free users ignored. If a free tier feeds paid conversions, the cost of serving free users is part of acquisition cost.
• Survivors only. Averages taken across current customers exclude everyone who already churned, which inflates retention. Use cohorts that include every customer who started.

End each review with one action per metric that moved the wrong way. RaiseMoney observes that metrics become more credible to investors when they visibly change behavior, such as stopping an expensive channel or changing onboarding after a review (RaiseMoney).