A soft hand contains an ace currently counted as 11. If another card would push the total over 21, the ace can change to 1. That flexibility makes hitting and doubling safer than they would be on the same hard total.
The pattern to learn
- Soft 13 and 14: double against 5 or 6; otherwise hit.
- Soft 15 and 16: double against 4 through 6; otherwise hit.
- Soft 17: double against 3 through 6; otherwise hit.
- Soft 18: double against 2 through 6, stand against 7 or 8, and hit against 9 through ace.
- Soft 19: double against 6 when allowed; otherwise stand.
- Soft 20: stand.
When a recommended double is unavailable, soft 18 falls back to stand; the lower soft totals fall back to hit.
Soft does not mean weak. It means the ace can still change value.