The New York Times’s paywall continues to outperform expectations at its first birthday. The paper says it now has 454,000 paying digital subscribers.

Those numbers are increasing at a healthy clip. Here are the numbers the Times has reported in the last year:

Second quarter: 281,000

Third quarter: 324,000

Fourth quarter: 406,000 390,000

First quarter 2012 (still underway): 454,000

You’d expect growth to slow after the first few months, since your most diehard readers will sign up right away when faced with losing access to the paper, but back when the NYT released those third quarter numbers, I worried that the rate of growth had fallen so sharply from the first full quarter of the paywall.

But the paper has added nearly 58,000 digital subscribers per quarter after that first quarter—a 17 percent clip per quarter, which is excellent. If the paper could keep that 17 percent growth rate up, it would have 850,000 digital subscribers by March 2013. It won’t, simply because growth (of anything, not just circulation) gets harder as a number increases. Still, it’s reasonable to think that the paper might grow at half that rate on average for the next four quarters. That would leave it with 629,000 a year from now.

That number is doable, particularly with the second part of the Times’s announcement today: That it’s making its leaky paywall less leaky. I wrote this a year ago:

I suspect twenty free stories is too high, particularly when combined with the porous backdoor from social media. But it’s better to start off high and then gradually adjust it as the data comes in and you see what the effect is. And that’s a key thing to remember here: This is just a start. The details of the Times’s paywall this time next year will probably be a lot different than at startup. Expect the twenty free stories number to drop, for one. I think the multi-platform cost is way too high, too. It’s $15 for the Web, but $35 if you want to read the paper on your phone and iPad. I suspect that $35 will be closer to $15 than anything by six months or a year from now. The Times was smarter in giving print subscribers free access to all digital platforms. That will help preserve print circulation for those of us who are heavy hybrid readers.

I’m glad to have been wrong on both counts here. Twenty free stories a month was not too many to discourage people from paying for digital subscriptions. But the logic stands: As the paywall limit hits more readers, more will cough up the cash to pay to read the Times. The paper might goose its growth rate a bit over what it would have been, though I’d guess it would goose it more by figuring out how to block those workarounds that tech-savvy readers use to avoid the paywall.

I wonder, though, whether the Times would even want to fix it to where you can’t game the system. I’d guess the population that does this skews toward younger, tech-savvy people, and folks who just flat can’t afford $15 a month for a newspaper. Older people with disposable income aren’t going to want to bother removing URL code every time they look at a story—if they even know how to do it. The workaround then adds a sort of demographic leakiness to the paywall.

Anyway, these numbers are very, very good, not to mention the digital ad numbers, which have continued to rise. To get an idea of how much they surpass expectations, look at some of the numbers I guessed a year ago:

My guess is it will hit 100,000 digital subscriptions in the first few months and will far surpass that in a couple of years.

And I’m a longtime pro-paywall guy.

I also wrote this in October, after growth slowed sharply in the second quarter of the paywall:

It seems clear the Times isn’t going to have half a million paying digital subscribers this time next year.

It seems clear now that the Times might reach the 500,000 mark sometime next quarter, well before October.

We don’t know how much money the Times is bringing in from its paywall since we don’t know how much it’s discounting subscriptions as a marketing tactic. But it’s easily in the tens of millions of dollars.

Since this new revenue stream is so important for the future of the company, it’s time for the NYT Company to break out digital circulation revenue like it does digital ad revenue in its quarterly earnings reports.

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Ryan Chittum is a former Wall Street Journal reporter, and deputy editor of The Audit, CJR's business section. If you see notable business journalism, give him a heads-up at Follow him on Twitter at @ryanchittum.