Richard Suchenwirth 2017-10-07 - Below is the formula how German income tax is calculated for 2017, translated from the Excel macro given on https://de.wikipedia.org/wiki/Einkommensteuer_(Deutschland)#Tarif_2017 .
Note that the argument "e" stands for "taxable income" ("zu versteuerndes Einkommen", zvE), which is the gross income minus deductions for
The rules for deductions are not implemented, neither is "progression reservation" ("Progressionsvorbehalt").
I tested the code with corner values, and it looked plausible - but use it at your own risk...
proc de_ESt_2017 e {
if {$e > 256303} { #zone 5
set res [expr $e*0.45 - 16164.73]
} elseif {$e > 54057} { #zone 4
set res [expr $e*0.42 - 8475.44]
} elseif {$e > 13769} { #zone 3
set tmp [expr $e-13769]
set res [expr $tmp*($tmp*0.0000022376+0.2397) + 939.57]
} elseif {$e > 8820} { #zone 2
set tmp [expr $e-8820]
set res [expr $tmp*($tmp*0.0000100727+0.14)]
} else {set res 0.00} ;#zone 1
return $res
}AMG: I highly recommend to brace your expr-essions for performance, correctness, and security reasons.