Binary division, with reminder I'm trying to do a binary division to find a remainder. Here's what I've done: 10011100/1001 = 10001 1001 ---- 00001 0 ----- 11 0 ---- 110 0 ----- 1100 1001 ---- 0011 This gives me a remainer of 0011 or 3 in decimal, which is correct when dividing 156/9. However, when I'm using online calculators, they all give me a remainder of 101 or 5 in decimal. What am I doing wrong?

Both calculators are computing in GF(2), the Galois field of order $2$. In this field, subtraction does not involve carries -- subtraction is accomplished by XORing the operands.

For instance, at your first link, the last "subtraction" is "$1100 \underline{\vee} 1001 = 101$.

An actual binary calculator gets the result you are expecting.