Should a new SaaS charge from the first day?

Yes. Charge from the first customer. A price on day one is a fact about the product; a price introduced a year later is a betrayal of the people who trusted you, and they'll treat it like one.

I know because I ran a product free for 14 months.

The shopping list

It was a shared shopping list for households, built in 2 weeks, mostly for myself. I launched it free, because I'd read many times that the sensible way to start was to give a product away, see if people used it, and charge later. Validate first. It sounded humble and scientific, and it meant I didn't have to have the conversation about money.

People used it. It had more users than anything I'd ever built. I talked about it as though it were working.

In month 14 I put a small price on it, with plenty of warning. Almost everybody left.

What free users actually prove

Free users prove that people like free things. That's all. I knew it already about every human being alive.

What I needed to know was whether anybody would pay, and the only way to find out was to ask them to, on the first day, when the price would have been part of the product rather than a change to it. (Changes to a deal are what people remember.)

Free still costs you

Free users write to you exactly as often as paying ones. For most of that first year I answered every message within the hour: at 11 at night, on holiday, from a supermarket car park. Then, one month, I was tired and stopped answering at all, and a year of instant replies followed by a month of silence read as the product being abandoned.

That's the real cost of free. Not the hosting. The evenings.

If you want people to try it first

Use a trial with an end date, told to every user the day they join, and keep the date. That turns free into an experiment with an end, instead of a habit you eventually have to break, to people who trusted you.

Or offer a money-back promise. They pay from the first day; if it doesn't work for them in the first month, they get it back. The price is honest, and so is the risk.

Nobody Bought It has the shopping list's full autopsy. Ship Alone has the method for charging from day one.