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Often I see CAC:LTV prominently featured in pitch decks, but we rarely look at this metric opting instead to examine payback. Similar, but slightly different...Why? See below for thread on payback 
For early businesses, LTV relies on some churn assumption which may or may not be representative of what it will look like longer term. E.g. churn has been 2% monthly your first year, but who is to say that that is what it will be the 2nd, 3rd, etc. year?
Payback instead is based on actuals. How much did you spend per a given period of time (often monthly or quarterly) and how much new revenue/how many new customers did that result in? Can look at this on a cohort basis to see how customers are actually behaving over time.
There's different ways to calculate, but here's how we think about it: Sales & Marketing Expenses in
a given period divided by new MRR (both new and expansion) acquired in period * gross margin of given period. The "period" here is often equal to the length of sales cycle.
a given period divided by new MRR (both new and expansion) acquired in period * gross margin of given period. The "period" here is often equal to the length of sales cycle.
So what does "good" payback look like? Well naturally this will change over time as your business grows and evolves, but TLDR the faster the better. Most SaaS investors look at ~12 months as excellent, but it largely depends on your GTM motion and other business characteristics.
There's no one size fits all and payback is considered alongside things like logo and net retention. E.g. if you have long sell cycles, high retention, and large ACVs, your payback might be longer and that's not necessarily a bad thing.
BUT if you are a self-service model (quick sell cycle, low ACVs) with a long payback that might not be looked at as favorably. I could keep going, but I'll stop here for now 
