Zero.

The number of names on the NFL’s all-time list of greatest quarterbacks ahead of Tom Brady, and — per Brady — the percentage chance that Super Bowl 53 was the final game of his career. That means there are also zero items on the Patriots’ offseason to-do list that carry more importance than extending the contract of the 19-year veteran.

The move is essential for two reasons:

(1.) Brady hasn’t played a single down of football on the final year of an NFL contract — and his current deal expires after the 2019 season.

As wild as it once seemed, the notion of Brady playing into his age-45 season is no longer far-fetched. Regardless of how his current physical ability compares with the NFL’s other top-level quarterbacks and its young up-and-comers, Brady still checks all the necessary boxes in arm strength and accuracy, and he still possesses a lightning-quick release. There is no one better with regard to the cerebral pre and post-snap components of the position, and he is still second-to-none in terms intra-pocket awareness and progression management.

He’s won a league MVP and taken the Patriots to two Super Bowls since turning 40. New England has never been in the business of paying for a player’s past accomplishments, but while minor signs of a “decline” have appeared in momentary batches, there is little doubt that plenty of meat remains on the bone of Tom Brady’s career. He’s still providing top-level production at the most important position in sports, and the Patriots must take the necessary steps this offseason to secure his services for the foreseeable future.

(2.) Cap space.

By now it’s no surprise that the Patriots’ salary cap situation is tighter than usual to start the NFL’s offseason. Depending on the official 2019 league-wide salary cap number, Miguel Benzan of Boston Sports Journal projects New England’s current cap space number at $18,096,579. This doesn’t include items like retirements, the signing of the team’s draft class, tendering restricted free agent cornerback Jonathan Jones, or cutting players whose current cap hits are misaligned with their production. It also doesn’t include the signing of any unrestricted free agents, or other expenditures such as offseason workout bonuses, fielding a practice squad, or maintaining a cushion to replace players who go on IR.

As the “cap is crap” contingent often notes, the Patriots have a lot of ways to create cap space for themselves in 2019. But, many of those avenues include cutting or restructuring contracts for productive members of the roster like Adrian Clayborn and Dont’a Hightower, or relying on the potential retirements of Rob Gronkowski and Devin McCourty. Aside from the release of Dwayne Allen, a Brady extension has been the most most likely vehicle for creating additional cap flexibility for the organization this offseason.

While an extension for the 19-year veteran will almost certainly create some 2019 cap space, it’s not likely to be the beacon of salary cap refuge that many have long envisioned. Let’s take a look at some reasons and example of why.

First, to set a baseline, the most cap space that could possibly be created in 2019 by a Tom Brady extension is $11.176 million. Sounds fantastic, right? Here’s how that would go down.

The savings here are achieved by converting $13.97 million of the $15 million in cash that Brady was set to earn in 2019 into a signing bonus, and then prorating it over five seasons — two of which are voidable years that are only tacked on the end of the deal to maximize the impact of the proration. Brady’s 2019 cap hit would consist of a $1.03 million minimum salary, the previous $12 million signing bonus proration, and the proration from the new signing bonus — $2.794 million.

In this scenario, Brady wouldn’t take a dime less than he was already set to receive this season. The issue? This simply isn’t how the Patriots operate. They don’t add voidable contract years for short-term gain. It’s just bad economics.

Even when taking previous “discounts” that Brady has given the organization into account, this deal falls short of what he should command on a per-year basis. If the APY of his current deal, which was signed against a league salary cap of $155.27 million in 2016, were to be extrapolated to this year’s projected $190 million league cap figure, it would put Brady’s new extension in the $25 million per-year ballpark.

Of course, given Brady’s age, one could see his new deal coming up short of that per-year figure as a trade-off of sorts for the additional contract years. Along with a more team-friendly guarantee structure, the continued strong presence of per-game bonuses and incentives is practically a certainty as well.

Here’s what Brady’s final contract extension with the Patriots could look like.

In total, this new three-year deal would be worth up to $68.03 million with $28.03 million guaranteed at signing. In order to decrease his cap figure this year, Brady’s existing 2019 per-game bonuses have been scrapped, and $12.97 million of his 2019 salary has been rolled into a $27 million signing bonus that is prorated over the deal’s three seasons.

The guaranteed-at-signing portions of the deal are the signing bonus and his $1.03 million veteran minimum salary in 2019. However, $5 million of Brady’s 2020 salary is guaranteed for injury only, and if the Patriots were to pick up the $5 million roster bonus in 2020 (due on the first day of the league year), his entire 2020 salary would then become fully guaranteed.

This deal would show the team’s tremendous confidence in Brady’s ability to continue performing at or around the same level for the next two seasons, but they are also insulated fairly well in terms of risk. Brady’s per-game bonuses would start again in 2020, and $3 million worth of incentives — which would be tied to to personal and team performance — would also start in 2020.

If Brady’s skill set were to deteriorate rapidly over the course of the 2019 season to the point where the Patriots would want to move in a different direction, they could decline his $5 million option and lose only $1 million in net cap space in 2020 after accounting for his $18 million in dead money. They could also decline his option and release him with a June 1st designation, saving $8 million in 2020 cap space with $9 million in dead money hitting the books in 2020 and 2021.

This extension helps the Patriots now as well — to the tune of $4.97 million in 2019 cap savings. It’s not the massive chunk that many dreamed of, but with how Bill Belichick and Nick Caserio stretch a dime, it just might make all the difference when all is said and done.

More importantly, the contract would keep Tom Brady in a New England Patriots uniform for two extra seasons and keep the organization’s “window” wide open as they continue to build on the greatest dynasty that professional sports has ever seen.

Follow Brian Phillips on Twitter @BPhillips_SB