Identifying the highest-paid NFL players annually is more difficult than with their counterparts in the NBA and MLB. NFL contracts are often front loaded because the deals aren't fully guaranteed. This creates more variance on a year-to-year basis.

Most attempts to determine the highest-paid football players in a particular year are imprecise. Salary deferrals aren't considered. Taxes aren't factored into the equation either.

Salary deferrals

Salary is usually deferred in the most lucrative NFL contracts. Typically, when a player has a large signing bonus in his contract, he doesn't receive a portion of the bonus until the next calendar year.

This is a well-established practice in the NFL. Peyton Manning's seven-year, $98 million contract with the Colts from March 2004, which made him the NFL's highest paid player (by average salary), included a $34.5 million signing bonus; $18.5 million of the $34.5 million wasn't paid to Manning until March 2005.

Several players who signed contracts in 2018 got large signing bonuses. These are usually broken into two to four installments rather than paid in a lump sum, regardless of whether all of the money is received in the same calendar year the deal was made. The overwhelming majority of these players will be receiving payments from their signing bonuses in 2019. The biggest deferrals and payment dates are in the following chart.

Note: Garoppolo's $28 million is a 2018 third-day-of-the-league-year roster bonus

Rams interior defensive lineman Aaron Donald isn't among 2018's highest-paid NFL players despite his $40 million signing bonus being the most ever for a non-quarterback because of the payment schedule: $10 million was paid within 10 days of Donald signing a six-year, $135 million contract extension in early September to become the NFL's first $20 million-per-year non-quarterback. On Oct. 1, $5 million was paid. Donald is due the remaining $25 million next March. With 62.5 percent of the $40 million payable next year, Donald will certainly be one of 2019's highest-paid players considering he is also scheduled to make a fully-guaranteed $9.108 million in base salary.

(Stream all of Sunday's NFL games on fuboTV, try it for free, and stream the CBS games on CBS All Access.)

Taxes

Taxes for professional athletes are more complicated than for people in most other professions because their income is earned in the states where they play. Athletes are required to file taxes in their home state and practically every state where they play a game according to Robert Raiola (@SportsTaxMan on Twitter), who is the director of the Sports and Entertainment Group at accounting firm PKF O'Connor Davies. Raiola named Detroit, Cleveland, Cincinnati, St. Louis and Kansas City as cities that also tax athletes.

The only states where NFL teams are located that don't have a state income tax are Florida, Tennessee, Texas and Washington. Raiders players will begin seeing an increase in their take-home pay once the franchise relocates to Las Vegas in 2020 since there isn't a state income tax in Nevada.

California has the highest tax rate in the country at 13.3 percent when income is at approximately $1 million. According to Raiola, an athlete who plays for a California team and is also a resident will likely be paying over 50 percent of his salary in income taxes.

The Tax and Job Cuts Act of 2017, which became effective on Jan. 1, is having a significant impact on athletes. The good news is the top federal tax rate dropped from 39.6 percent to 37 percent. The gains from this cut are being offset by the elimination of certain itemized deductions and a $10,000 cap on deducting state and local/property taxes. Raiola mentioned agent fees, training expenses, union dues and fines as items athletes can no longer deduct.

Sorry to interrupt your reading, but just a quick PSA here. We have a pretty amazing daily NFL podcast you may not be aware of. It's hosted by Will Brinson and it's all the things you're looking for: news, fantasy, picks, really, just football stuff for football people. Subscribe: via iTunes | via Stitcher | via TuneIn | via Google

Top earners

I enlisted the help of Raiola to provide his expertise for the tax calculations in determining the 15 highest-paid NFL players for 2018. The chart is below.

Endorsement and marketing income have been excluded. All federal and state taxes are included in the calculations, along with marital status. The tax implications of playing in a game in London or charitable contributions aren't factored into the equation. Playoff money isn't included in salary but any incentives earned in 2017 have been, since payment occurs in 2018.

Players are assumed to be a resident of the state and city where they play. Since players typically live near the team facility, New Jersey is considered the state of residence for members of the Giants and Jets.

Vikings quarterback Kirk Cousins is the lone exception. Michigan is being used for Cousins because he built a house there in 2017. According to Raiola, Michigan and Minnesota have a reciprocal agreement. This allows Cousins to pay the lower Michigan tax rate of 4.25 percent instead of Minnesota's 9.85 percent.

An additional assumption is being made. Players will receive final payment of their base salary and applicable per-game roster bonuses in 2018 since the last regular-season game is on Dec. 30.

Packers quarterback Aaron Rodgers' $66.9 million is unprecedented in North American team sports. To put it in perspective, the most an NBA player has ever made before taxes from his playing contract is Golden State Warriors guard Stephen Curry's almost $37.5 million for the current 2018-19 season. The largest contracted NBA salary is the $46.872 million Houston Rockets guard James Harden, the reigning NBA Most Valuable Player, is scheduled to make for the 2022-23 season.

Most of Rodgers' compensation comes from his NFL-record $57.5 million signing bonus. Unlike most teams, the Packers routinely pay signing bonuses, regardless of the amount, in the calendar year of signing. Rodgers received $13 million of the $57.5 million within 10 days of signing a four-year, $134 million contract extension in late August, averaging $33.5 million per year, which makes him the NFL's highest paid player. $37 million is being paid concurrently during the regular season with his base salary. The remaining $7.5 million is due to Rodgers on Dec. 26.

Rodgers' salary after taxes is just over $700,000 more than that of the second-highest-paid player, Redskins quarterback Alex Smith's $35 million pre-tax salary. The Packers quarterback is unlikely to be among the NFL's highest paid in any given year for the remainder of his contract. His 2019, 2020, 2021, 2022 and 2023 pre-tax salaries are $15 million, $21.1 million, $22 million, $25.5 million and $25.5 million.

Matthew Stafford was the previous signing-bonus record holder at $50 million. Of the Lions quarterback's $50 million -- which pertains to his then NFL record 2017 contract extension averaging $27 million per year -- $16.5 million wasn't paid until this past February. He is the lone player among the 15 highest paid with money from a signing bonus deferral. Stafford and Raiders quarterback Derek Carr are the only two players on the list who signed contracts in 2017.

There isn't much movement among the highest-paid players in pre-tax earnings and salary after taxes. The most variance occurs with the Californians, 49ers quarterback Jimmy Garoppolo and Carr. Garoppolo went from fourth before taxes to seventh after taxes. Carr dropped four spots to 14th when taxes are taken into account. Garoppolo's $31.95 million pre-tax earnings are $4.95 million more than Saints quarterback Drew Brees' $27 million. He is a little more than $225,000 behind Brees after taxes.

Cowboys offensive guard Zack Martin is a perfect illustration of the benefit from playing in a place, Texas, without a state income tax. Giants offensive tackle Nate Solder and Martin are both at $22 million before taxes. Martin's net dollars are almost $2.175 million more than Solder's.

Giants running back Saquon Barkley, the second-overall pick in the 2018 NFL draft, is the only rookie in the top 15, although the Browns selected quarterback Baker Mayfield No. 1. Of Mayfield's $21,849,440 signing bonus, $7,649,440 isn't payable until the end of January 2019.

Third-overall pick Sam Darnold was 14th before taxes with $20,558,324. The Jets quarterback drops to 19th after taxes.