D2C in Vietnam is in a favourable phase: channels are easy to open, numbers are easy to move, and the feeling of growth is easy to create. That is exactly why many brands do not know where they are losing money until the cash runs out. The right question is not "are my unit economics good" but "at this stage, which number should I be watching".

Before product-market fit: do not optimise, measure honestly

The common mistake here is optimising too early. You do not yet know who truly needs the product, yet you are already worried about cutting CAC. The one thing worth measuring precisely at this stage: does anyone buy a second time, and why. Without a real retention signal, every CAC and LTV figure is a guess, because you do not yet know what a customer is worth.

After product-market fit, scaling: watch CAC payback

This is when unit economics start to decide the outcome. The first number I look at is not LTV to CAC, which is easy to present well, but CAC payback: how long a customer takes to repay the cost of acquiring them. If payback runs longer than your cash can carry, faster growth brings the cash-out point closer, even while the accounts show a gross profit.

The warning threshold I use for Vietnamese D2C: payback beyond four to six months without long-dated capital is the point to stop increasing ad spend and re-examine the model, not the point to accelerate.

Growing fast: beware numbers that look good but are not real

Three traps when the numbers are rising:

  • Blended CAC hides the weak channel. The average looks fine while one channel is losing heavily, carried by organic. Split each channel out and you will see where the money is going.
  • Repeat revenue that is really repeat discounting. Customers return for the discount, not the product. Stop the promotion and they leave. That is not retention. It is revenue bought with margin.
  • Inventory absorbing all the cash. Profitable on the income statement, but the money sits in the warehouse. Many brands that spike and cannot recover die of cash flow, not of losses.

A quick self-check

You do not need to hire anyone to start. Split CAC by channel, compute payback for your largest channel, and answer honestly: if every promotion is switched off next month, how much revenue remains. Those three numbers are usually enough to know whether the business is healthy or bleeding.

For a more systematic check, I have a free D2C health diagnostic: 22 rules across 5 pillars, 10 minutes, no email required. It does not replace a real conversation, but it is enough to show where things are breaking.