Pay per day as in charging a credit card each day?

It is likely the credit card will flag your company as a scam. No one wants to see their credit cards charged on a day-by-day basis, either, and I think you'd be covering those fees (2.5% + 0.30 for Paypal and Stripe).

I've gone into Walmart, forgotten to buy something, had to go back, and while the second time usually goes through, I get declined after that. I've driven across the country and instead of filling my gas tank up half way or when it gets to E, I've attempted to fill it up every 20 miles or so, even every time I saw a gas station, and my credit card got flagged and I had to wait 24 hours to for them to unblock it.

I know we're talking in terms of minutes to hours here, but "day-by-day" with a charge for the same company may get flagged.

I've been charging on a monthly basis (which Stripe can do automatically) and I've even seen people doing 3-6-9-12 month basis, but there is another method that I'm planning to use, which I haven't seen much. While Stripe doesn't officially support it, there are methods to actually get it to work which allows you to "pay as you go." (PayGo)

In this way, at the end of the month (simply grab the 1st day of the month and subtract by 1 or grab the last day of the month at 11:59:59 PM) and you calculate how much a person used for the entire month. Then you would just change the invoice to reflect the new charges. In my future projects, I will probably start going this route.

I'd think people wouldn't mind putting in their credit card and then just getting charged for what they used (once per month). It is more peace of mind too...

Saas is like: use it or lose it.

Pay as you go is... use it or don't.

As far as my method of building web apps go: I offer X amount of something for free. After that a month, it returns back to the original X and as the person uses it, it counts down until there are no more, and then you have to wait a month to use more of it. If you want more, I offer 2 solutions: subscribe for more or refill your X on the "free" plan which just gives you more without the added benefits of the higher plans.

Users won't think of the cost every day but they'll notice different monthly charges on their credit card statement and wonder how they can save money then. Worse for B2B when changing amounts raise questions from other departments and need to be re-approved or justified.

How about plans that cover 15 transactions, 30, 100 and users can take over any unused transactions to the next month? I've seen services where you pre-pay packages of 100 or 500 (text message sending, Skype minutes) even which will lead to irregular payments on your end.

I think for tax purposes you need to set aside income from unused transactions. That's why often in the fine-print it says they can expire or loose value over time.

Personally I'd do monthly plans though. Some users will overpay or even forget they signed up. In that case offer generous free refunds or even email them if they haven't used the service a certain amount of days/months and offer to cancel for them.

I personally would not pay-per-day if its 1 transaction/day.

Now, that being said, you could set up monthly transactions which are calculated on a daily basis.

Somewhat related: Tarsnap has a weird pricing scheme. You can follow the advice of patio11 in http://www.kalzumeus.com/2014/04/03/fantasy-tarsnap/ HN discussion https://news.ycombinator.com/item?id=7523953 (801 points, 1202 days ago, 311 comments) or you can follow the example of cperciva and ignore patio11.