Rex says
Money math without the spreadsheet headache. Plug in your numbers and I'll show you exactly where the dollars land.
Try a scenario
Click to load — tweak from there.Inputs
Result
Blended payback after shift
3.9
Current blended payback (months)
4.3
Channel A payback (months)
3.4
Channel B payback (months)
6.3
Extra customers per month after shift
37.9
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How to use this
- 1Enter channel a monthly spend ($).
- 2Enter channel a cac ($).
- 3Enter channel b monthly spend ($).
- 4Enter channel b cac ($).
- 5Enter monthly gross profit per customer (both channels) ($).
- 6Enter budget to shift from slower to faster channel ($).
- 7Read your blended payback after shift on the right — it updates as you type.
- 8Hit Share to keep the scenario or send it to someone.
About this calculator
When budget is limited, the highest-ROI allocation usually isn't spreading dollars evenly or chasing the lowest CAC in isolation — it's ranking channels by how fast they return cash (payback period) and funding the fastest-payback channels first until they saturate, then moving down the list. This calculator takes up to four channels with their monthly spend, CAC, and monthly gross profit per customer, computes the payback period for each (months to recover the CAC from gross profit), ranks them fastest to slowest, and shows what happens to blended payback if you shift a fixed amount of budget from the slowest-payback channel to the fastest. Fast payback matters disproportionately for cash-constrained businesses, since a channel with a 2-month payback recycles capital into new growth spend six times a year, while a 12-month payback channel ties up cash for a full year before you can reinvest that same dollar, even if its terminal LTV is comparable. Growth-stage companies with ample runway can tolerate slower-payback channels for their higher absolute LTV, but bootstrapped or cash-tight operations should weight payback speed heavily in the allocation decision.
Worked example
Using the values the calculator loads with:
Inputs
- Channel A monthly spend: 40000 $
- Channel A CAC: 120 $
- Channel B monthly spend: 30000 $
- Channel B CAC: 220 $
- Monthly gross profit per customer (both channels): 35 $
- Budget to shift from slower to faster channel: 10000 $
Results
- Blended payback after shift: 3.9
- Current blended payback (months): 4.3
- Channel A payback (months): 3.4
- Channel B payback (months): 6.3
- Extra customers per month after shift: 37.9
What each field means
Inputs
- Channel A monthly spend ($)
- The channel a monthly spend used in the calculation, measured in $. Starts at 40000 $ so you have a working example on load.
- Channel A CAC ($)
- The channel a cac used in the calculation, measured in $. Starts at 120 $ so you have a working example on load.
- Channel B monthly spend ($)
- The channel b monthly spend used in the calculation, measured in $. Starts at 30000 $ so you have a working example on load.
- Channel B CAC ($)
- The channel b cac used in the calculation, measured in $. Starts at 220 $ so you have a working example on load.
- Monthly gross profit per customer (both channels) ($)
- The monthly gross profit per customer (both channels) used in the calculation, measured in $. Starts at 35 $ so you have a working example on load.
- Budget to shift from slower to faster channel ($)
- The budget to shift from slower to faster channel used in the calculation, measured in $. Starts at 10000 $ so you have a working example on load.
Results
- Blended payback after shift
- Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Current blended payback (months)
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Channel A payback (months)
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Channel B payback (months)
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Extra customers per month after shift
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
Why prioritize payback speed over total LTV?
For any cash-constrained business, the speed at which you get money back determines how fast you can reinvest and compound growth. A channel with faster payback but similar or slightly lower LTV lets you run more growth cycles per year with the same capital base.
When should I ignore payback and chase LTV instead?
When you have ample runway or committed funding and the fast-payback channel is a smaller, saturating pool while the slower-payback channel has far larger scalable volume and comparable or better long-run LTV. Growth-stage companies optimizing for market share often accept slower payback deliberately.
What counts as monthly gross profit per customer?
Revenue per customer per month minus cost of goods, fulfillment, and payment processing — before marketing spend. For a one-time-purchase business, spread the total gross profit of the average order across the expected months until repeat purchase or churn.
How many channels can I model at once?
This calculator compares two at a time for a clean shift analysis; for a full multi-channel allocation, rank every channel's payback with the same formula and greedily fund from fastest to slowest until you hit total budget or channel saturation.
Accuracy and limitations
- Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
- Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.
- This is educational maths, not financial advice. Check anything contractual with the lender or your accountant.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Marketing Budget Allocation by Payback Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/marketing-budget-payback-allocator
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/marketing-budget-payback-allocator" target="_blank" rel="noopener">Marketing Budget Allocation by Payback Calculator — RevenueLab</a> (2026).</p>
Source: [Marketing Budget Allocation by Payback Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/marketing-budget-payback-allocator) (2026).