Federal income tax calculator for procrastinators

Question

Today is Tax Day!

Oops.

Well, today is tax day if you are a resident of Maine or Massachusetts.

So you're probably still completing your return and need a calculator for when you get to Line 44.

Given an input of taxable income (US$, accurate to 2 decimal places) and a string representing filing status, output the amount of tax (also US$ to 2 decimal places).

Filing status will be one of S, MFJ, QW, MFS, or HH for Single, Married Filing Jointly, Qualified Widow(er), Married Filing Separately or Head of Household, respectively.

• Tax will be calculated according to the official tables in IRS Revenue Procedure 2014-61, section .01 Tax Rate Tables, Tables 1-4. I have added these tables at the bottom of the question.

• You may choose whatever rounding method you like, as long as the result is accurate to 2 decimal places.

Example Inputs:

0.00 S
10000.00 MFJ
100000.00 MFS
1000000.00 QW

Example Outputs corresponding to above inputs:

0.00
1000.00
21525.75
341915.90

---

Summary of tax tables.

Married Filing Jointly and Qualified Widow(er)

Income Interval Tax [ $0, $18450] 10% ( $18450, $74900] $1845 + 15% of the excess over $18450 ( $74900, $151200] $10312.50 + 25% of the excess over $74900 ($151200, $230450] $29387.50 + 28% of the excess over $151200 ($230450, $411500] $51577.50 + 33% of the excess over $230450 ($411500, $464850] $111324 + 35% of the excess over $411500 ($464850, $∞] $129996.50 + 39.6% of the excess over $464850

Head of Household

Income Interval Tax [ $0, $13150] 10% ( $13150, $50200] $1315 + 15% of the excess over $13150 ( $50200, $129600] $6872.50 + 25% of the excess over $50200 ($129600, $209850] $26722.50 + 28% of the excess over $129600 ($209850, $411500] $49192.50 + 33% of the excess over $209850 ($411500, $439000] $115737 + 35% of the excess over $411500 ($439000, $∞] $125362 + 39.6% of the excess over $439000

Single

Income Interval Tax [ $0, $9225] 10% ( $9225, $37450] $922.50 + 15% of the excess over $9225 ( $37450, $90750] $5156.25 + 25% of the excess over $37450 ( $90750, $189300] $18481.25 + 28% of the excess over $90750 ($189300, $411500] $46075.25 + 33% of the excess over $189300 ($411500, $413200] $119401.25 + 35% of the excess over $411500 ($413200, $∞] $119996.25 + 39.6% of the excess over $413200

Married Filing Separately

Income Interval Tax [ $0, $9225] 10% ( $9225, $37450] $922.50 + 15% of the excess over $9225 ( $37450, $75600] $5156.25 + 25% of the excess over $37450 ( $75600, $115225] $14693.75 + 28% of the excess over $75600 ($115225, $205750] $25788.75 + 33% of the excess over $115225 ($205750, $232425] $55662 + 35% of the excess over $205750 ($232425, $∞] $64998.25 + 39.6% of the excess over $232425

Answer 1

Python 3, 427 382 317 309 308 275 bytes

-45 bytes by figuring ternary expression out (wow that's a long line); thanks Maltysen

-65 bytes, now with iteration for DRYer code!

-8 bytes by in-lining tuple variables; thanks Majora

-1 byte by using a dict rather than ternary chain; thanks again Maltysen

-33 bytes by reusing MFS step as half of MFJ/QW and calculating tax an order of magnitude larger; thanks Neil

def f(i,s):
 t=i;k={'MFS':(9225,28225,38150,39625,90525,26675),'S':(9225,28225,53300,98550,222200,1700),'HH':(13150,37050,79400,80250,201650,27500)}
 for x in range(6):
  i-=k[s][x]if s in k else k['MFS'][x]*2
  if i>0:t+=(.5,1,.3,.5,.2,.46)[x]*i
 return'{:.2f}'.format(t*.1)

If I had been thinking I would have made the function signature t(a,x), but I guess I'll stick with function(income, status).

When code is barely undertstood by the writer, is that when you win at golf?

Answer 2

JavaScript (ES6), 223 bytes

(i,s)=>(({MFS:a=[x=9225,y=28225,38150,39625,90525,26675],S:[x,y,53300,98550,222200,1700],HH:[13150,37050,79400,80250,201650,27500]}[s]||a.map(b=>b*2)).reduce((t,b,j)=>t+((i-=b)>0&&i*[.5,1,.3,.5,.2,.46][j]),i)*.1).toFixed(2)

Basically a port of CAD97's Python answer, but I saved 4 bytes by multiplying the tax by 10 during the calculation and 11 bytes by reducing the duplication in the tax bands.