We investigate the tax burden and insurance cost for different scenarios of gross income using a simplified model of the situation in Germany. The goal is to compute the marginal net income for additional gross income. From that, we can also derive the net hourly income for part-time employment.
# assume a typical monthly income gross_monthly = 37873 / 12
For simplicity, we ignore the possibility of private health insurance and assume that our typical employee participates in the public social system. This includes health insurance, unemployment insurance and payments to the pension system.
These payments are split evenly between the employer and employee. This means that the labor cost of the employer is higher than the gross salary paid.
# only includes the employee's share pension = 0.186 unemployment = 0.03 health = 0.146 longterm_care = 0.028 base_rate = 0.5 * (pension + unemployment + health + longterm_care) health_extra = 0.011 employer_rate = base_rate employee_rate = base_rate + health_extra @show employer_rate, employee_rate;
(employer_rate, employee_rate) = (0.195, 0.20600000000000002)
# effective labor cost for employer real_monthly = (1.0 + employer_rate) * gross_monthly
However, these relative rates are only applied up to specific bound for the gross income. So, let's define some functions to compute the correct costs.
In the case of self-employment, there is also a virtual minimum income that is used as a reference, which we will ignore for simplicity.
function social_cost(gross_monthly) pension = 0.186 * min(gross_monthly, 6500.0) unemployment = 0.030 * min(gross_monthly, 6500.0) health = 0.146 * min(gross_monthly, 4425.0) longterm_care = 0.146 * min(gross_monthly, 4425.0) pension + unemployment + health + longterm_care end employer_cost(gross_monthly) = 0.5 * social_cost(gross_monthly) employee_cost(gross_monthly) = 0.5 * social_cost(gross_monthly) + 0.011 * gross_monthly total_cost(gross_monthly) = employer_cost(gross_monthly) + employee_cost(gross_monthly) employer_total(gross_monthly) = employer_cost(gross_monthly) + gross_monthly;
Let's visualize the total social cost relative to the real monthly labor cost.
using Plots gr()
gross_range = 400.0:20.0:10000.0 real_income = employer_total.(gross_range) relative_cost = total_cost.(gross_range) ./ real_income plot(real_income, relative_cost, xlim=(0,11000), ylim=(0.0, 0.5), legend=false, xlabel="effective monthly income", ylabel="rel social cost")
So, higher gross (or effective) income leads to a smaller relative social cost. We can repeat that plot for the employee's point of view:
plot(gross_range, employee_cost.(gross_range)./gross_range, xlim=(0,10000), ylim=(0.0, 0.3), legend=false, xlabel="gross monthly income", ylabel="employee's share of social cost")
The income tax only applies to the part of the gross income of which the social cost has been subtracted already. Further, some portion of that remainder is also free from taxes.
taxable_income(gross_monthly) = gross_monthly - employee_cost(gross_monthly)
taxable_income (generic function with 1 method)
The tax rate is a piece-wise defined function. We assume an unmarried employee with no kids who is not taxable by any church.
The source below actually contains flow charts with details conditions, thresholds and rounding of intermediate results. I can't be bothered to understand all of that, so I will try to extract the essential information.
Source: BMF Steuerrechner
function income_tax(yearly) if yearly <= 9000 return 0 elseif yearly < 13997 y = (yearly - 9000) / 10000 rw = y * 997.8 + 1400 return ceil(rw * y) elseif yearly < 54950 y = (yearly - 13996) / 10000 rw = y * 220.13 + 2397 return ceil(rw * y + 948.49) elseif yearly < 260533 return ceil(yearly * 0.42 - 8621.75) else return ceil(yearly * 0.45 - 16437.7) end end
income_tax (generic function with 1 method)
yearly_range = 5000:500:100000 plot(yearly_range, income_tax.(yearly_range), legend=false, xlim=(0,100000), ylim=(0,35000), xlabel="yearly taxable income", ylabel="income tax")
plot(yearly_range, income_tax.(yearly_range) ./ yearly_range, legend=false, xlim=(0,100000), ylim=(0,0.4), xlabel="yearly taxable income", ylabel="income tax rate")
function net(gross_monthly) taxable = taxable_income(gross_monthly) taxes = income_tax(ceil(12 * taxable)) / 12 taxable - taxes end net_income = net.(gross_range) plot(gross_range, net_income, legend=false, xlim=(0,10000), ylim=(0,6000), xlabel="monthly gross income", ylabel="monthly net income")
This looks surprisingly linear. Let's also plot the relative net income compared to the effective cost.
rel_net = net_income ./ real_income plot(real_income, rel_net, legend=false, xlim=(0,12000), ylim=(0,0.7), xlabel="effective monthly income", ylabel="rel net income")
Interestingly, this curve is not monotonically decreasing. In fact, there seems to be a minimum at a gross income of 4425 (real income of about 5300), which is the upper reference value for the health insurances.
The analysis above can be slightly misleading. If we are currently earning a certain income and have an opportunity to raise the income, this might also decrease our relative net income. However, higher rates for social cost and income tax are applied equally to the previous and additional income.
If we want to show how much net income we can retain for each additional EUR earned, we have take some more care. Here, we approximate the slope of the net income as a function of real income using a symmetric difference quotient. There are some jumps in that curve since our net income is not smooth.
finite_diffs = (net_income[3:end] - net_income[1:end-2]) ./ (real_income[3:end] - real_income[1:end-2]) plot(real_income[3:end], [finite_diffs rel_net[3:end]], xlim=(0,12000), ylim=(0,0.65), xlabel="effective monthly income", label=["marginal income" "relative net income"], legend=:bottomright)
Part-time work and hourly income¶
We have seen that a lower gross income often corresponds to a higher relative net income. If we have the option to reduce our working hours, we should be able to increase our income per hour.
Let's assume a 40 hour work-week and 4 weeks per month.
monthly_hours = 40.0 * 4.0
# median income median_net = net(gross_monthly)
median_net / monthly_hours
# hourly income for different monthly gross incomes hours = 10:40 steps = 6 gross = range(1000, stop=8000, length=steps)' colors = ColorBrewer.palette("YlGnBu", steps + 3)[4:end] parttime_net = net.((hours / 40)*gross) hourly_net = parttime_net ./ (hours * 4) plot(hours, hourly_net, labels=gross, ylim=(0,40), color_palette=colors, xlabel="hours per week", ylabel="hourly net income", title="Hourly net income for part-time work")
As we can see above, we can increase our hourly income by working fewer hours every week. This effect is more clear if we look at the hourly net income of part-time work relative the hourly net income for full-time work:
rel_hourly = hourly_net ./ hourly_net[end, :]';
plot(hours, rel_hourly, labels=gross, color_palette=colors, xlabel="hours per week", ylabel="relative hourly net income", title="Relative hourly net income for part-time work")
For low values of gross income, reducing the weekly work hours will not affect the hourly income any more. Medium values show the most promise, with the largest inrease in hourly income. With a high enough income, reducing the work load yields less and less increase in hourly income.