D/E ratio = Total Debt ÷ Total Equity. A D/E of 1.0 means the company owes as much as its shareholders own.
For most non-financial companies, a D/E below 0.5 is comfortable, 0.5–1.0 is manageable, above 1.5 is fragile.
Debt magnifies both good and bad years. In a boom, borrowed money boosts profits. In a downturn, the interest bills don't pause.
Exceptions: banks and NBFCs run on high leverage by design — the metrics look different for them.