Remainder
Residual
noun, の adjective
The remaining surplus is the remainder or residual left over.
Just bear in mind that this is a technical word that you'll mostly see in legal and financial contexts.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
倒産後、残余財産が残れば分配されます。
After bankruptcy, any remaining assets will be distributed.
「残余リスクについてもちゃんと議論したんですか？」「まだです。みんな残余リスクの計算式を忘れてしまって、議論にならないんです。」
"Have you guys discussed the residual risks, too?" "Not yet. We all forgot the formula to calculate residual risk, so we can't have the discussion."
今月の差額残余額は現時点でいくらになっていますか。
What is the this month’s remaining balance as of now?