If I misunderstood, I hope mawmawgal will be more specific.
She's not taking 1/2 a pill; the dosage 0.5 mg which is = to 50 mcg. She's asking how many 50 mcg pills to take to equal 125 mcg. It would take 2 - 50 mcg pills to make 100 mcg, then another .5 of a 50 mcg pill to make the other 25 mcg.
The dosage says .5 tablet of the 125mcg which would be 62.5mcg - 1 and a quarter of the 50 mcg.
Because the medication is relatively inexpensive, many of us just hang onto the medication when our dosage is changed, in case we need it at a later date. However, since the pills you have are 50 mcg, it would take 2.5 pills to make up the 125 mcg.
I must say that an increase that more than doubles your dosage, all at once is quite a lot. It's entirely possible that there's a dose in between that might work for you. Bumping up too quickly can often cause adverse reaction. I'd certainly advise caution.
Do you have current lab results that you could post, so member can better assess your testing and treatment? When posting labs, be sure to include reference ranges, which vary lab to lab, so have to be posted with results.