Payroll Withholding Tables- US & Canada (Jan 3)

2020 has been a double whammy year for payroll tax calculations.

IRS changed the W-4 form. Instead of the number of exemptions, it now uses a complex calculation that involves dependents, student loans, multiple jobs and gross income. The only good news is that you won’t have to deal with any of it until the first time you hire someone in 2020. Then it’s just a one-time setup hassle.

We had to add a second set of tax tables to support the new forms: instructions here. Payroll will be more complicated for the next 5 or 10 years, until the day when IRS stops allowing the old forms. Then we can delete the old tables, and it will be simpler again.

Meanwhile, Canada also made a big change, replacing the personal deduction with a step table. We had to create a custom option in 2002 just to calculate Canadian withholding, and this change breaks it.

Revenue Canada has an insanely complex system to calculate withholding. The formulas use almost every letter in the alphabet, plus K1 to K4, T1 to T4, and 20 multi-letter codes. Ten different TurtleSoft employees worked on it and failed, before one finally figured it out. We are still slogging through the instructions to see how to make the new setup work. One of the calculation options for US states looks promising as a substitute.

As math nerds, we get especially frustrated by complexities like this, because it’s totally unnecessary. Tax dudes, you only need a few numbers to make it work!

Six US states have a simple flat tax rate for everyone. Most have a deductible, so taxation starts at some income greater than zero.  If you graph tax withheld vs income, it will be a straight line. Two numbers are enough to define that: one for the zero point, and one for the slope. In algebra, it’s y = a + bx.

Sales tax, gasoline tax and most other taxes are regressive. Poor people pay a higher percentage of their income on them, because rich people spend more on non-taxable stuff like school tuition and tax shelters. To compensate, it’s reasonable to have a progressive income tax. That means higher earners pay a higher percentage. If you graph tax withheld vs income, it will be a curve.

Mathematically, you can define progressive tax curves with three numbers: zero point, slope, and curvature. In algebra, it’s y = a + bx + cx^2 (the ^2 means x squared).

However, using exponents makes it too scary for most people. The easiest alternative is a step table, with different rates for each range of extra income. If you graph payroll tax vs income, it will be a series of straight lines that approximate the desired curve. Data-wise, it only needs two numbers for each step: start point and slope.

For any desired ‘tax curve’, it’s possible to make a series of steps that are accurate enough for tax policy. Most US states do exactly that, using anywhere from 2 to 12 steps.

Unfortunately, a few states add all sorts of weird stuff to make it more complex. Connecticut is an extreme example, with 13 different step tables arranged 6 layers deep. Presumably the tax committee was stoned when they created the Table C 3% Tax Rate Phase-Out Add-Back. Canada has a related problem: they really need some good tech writers to redo the tax guide, so humans can understand it.

Thankfully, we only spend a few days a year on payroll tax tables. Our staff will soon be back to more productive work, programming regular tables for Goldenseal Pro.

Dennis Kolva
Programming Director





Author: Dennis Kolva

Programming Director for Turtle Creek Software. Design & planning of accounting and estimating software.