To calculate the amount of your childcare benefit take the negative of the your adjusted gross income (box 26a), divide it by 10,000, and add 2. Then take the arctan of that result and multiply by 5,000. Add 2500π and write the result in box 46. You may round the value of π to 2 digits. If you are filing as head of household, divide the amount in box 46 by the definite integral from 0 to your adjusted gross income (box 26a) divided by 10,000 of sin^2(x)/(x^2 + 1) dx, and write that amount in box 48. If you are unable to find the function of the anti-derivative, IRS rules allow you to approximate with a Riemann sum using the midpoint rule and a rectangle width of 0.1.

Or, as it has always been, piecewise linear approximate it.