A potential mathematical approach to equal taxation that works in any country:

1. Calculate the average income of every citizen. Let A = the average income (amount per year)
2. Set a baseline tax amount for the average (e.g. 10%). Let P = baseline tax percentage
3. Given a person’s income, calculate how far above or below they are compared to the average. Let I = a person’s income. We can calculate the difference, D, with D = I - A. A positive value means the person’s income is above average, whereas negative is below.
4. Calculate the difference as a percentage. Let Q = D / A
5. Calculate the percentage of the tax percentage. This will determine how much more or less a person will have to pay: R = Q * P
6. Finally, calculate the person’s unique tax amount: T = P + R. If R was a positive value, that means the person will pay more. If R was a negative value, they pay less. If R = 0, they pay the base amount.

Example: Let’s say the average income per year is $50,000 USD, and the baseline tax rate is 10%

So A =50,000 and P = 10% / 100 = 0.1

Given a person’s income: $30,000/yr:

I = 30,000

Calculate the difference:

D = 30,000 – 50,000 = –20,000 Q = –20,000 / 50,000 = –0.4 (–40%)

Calculate how much more/less the person pays:

R = –0.4 * 0.1 = –0.04 (–4%)

Calculate the unique tax amount:

T = 0.1 + (–0.04) = 0.1 – 0.04 = 0.6 (6%)

There might be a better set of formulas, but this is what I came up with. Let me know if I made a mistake in my math.