remote sensing - Landsat8 DN to TOA Reflectance (minus values)

I'm learning how to perform atmospheric correction manually, hence not using the automated methods available in ENVI

metadata (band 1) for my Landsat 8 scene is as follows;

RADIANCE_MULT_BAND_1 = 1.2344E-02

RADIANCE_ADD_BAND_1 = -61.72016

REFLECTANCE_MULT_BAND_1 = 2.0000E-05

REFLECTANCE_ADD_BAND_1 = -0.100000

SUN_ELEVATION = 48.12237303

So when I use band math to calculate TOA Radiance I type in this:

(0.012344*B1)-61.72016

And it yields a spectral statistics that look kind-of right

When I use any of the following band math formulae;

TOA Reflectance (excluding sun elevation adjustment)

(B1*0.00002)-0.1

TOA Reflectance (including sun elevation adjustment)

((B1*0.00002)-0.1)/0.74457226676389733207607359928648

Or calculate straight from the raw DN to TOA Reflectance (including sun elevation adjustment)

((((0.012344*B1)-61.72016)*0.00002)-0.1)/0.74457226676389733207607359928648

I end up with something like this:

which looks incorrect.

I've googled and either my search terms are rubbish or no one uses manual band math to do this.

[EDIT]

Mikkel's answer below with the revised band math calculation (omitting the intermediate steps) yielded the following statistics:

which look somewhat more realistic.

Wondering if i should add 13.4305 to each band, or ignore the negative minimum?

[END EDIT]

[EDIT #2]

Mikkel was spot on again, in suggesting that the -13.4305 values were isolated to the "no data" areas around the image;

as you can see, isolated only to the northern edge of the scene.

[END EDIT #2]

Answer

One flaw in your approach. You don't need to go through DN to radiance.
You can go straight to the DN to reflectance.
Just stick to ((B1*0.00002)-0.1)/0.74457226676389733207607359928648.