Play-by-Play: Variable Costs and Margins

May 30, 2010 by Craig

I did the revenue analysis; now it’s time for the expenses.

Variable Costs

These are expenses that are directly proportional to the number of customers you have. More customers = more variable costs.


For a cloud-based web application, the costs are pretty small. Heroku charges dyno can handle around 10 to 50 customers per second. Given that I’m only expecting 250 non-heavy-duty customers total, the variable costs should be tiny. I’d guess that the app could be hosted for less than $100/month, or $1200 a year. The cost per customer is about $5 per year. Chump change.

Payment Fees

I’ll need a merchant account to accept credit cards. I have some quotes for roughly 15 cents + 3% per transaction + $30/month (though the actual amounts vary a bit with provider, volume, and monthly fee). That’s about $4700/year, though with this sort of volume I could probably get a lower transaction fee for lower overall costs. It’s also about $19 per customer per year.


Over and above the merchant account fees are the payment gateway fees. I’m looking at Chargify as it has a good reputation. It costs $50 for up to $500 users; for my 250 users that’s $0.20/user… basically not worth considering.

Gross Margin

So if revenue per customer is about $520 per year, and the variable costs per customer are $25 per year, then the gross yearly margin per customer is $495. The margin rate is an astonishing 95%. For reference, a lot of businesses run on margins of 20% or less; really high-volume ones often have margins in the low single digits. That’s the beauty of software: once you build the thing, it costs nearly nothing to supply it to your customers.

Next up: fixed costs.

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