Jan Kukal has found clay courts difficult, recording 31–39 across 70 matches (44.3%). The numbers point to a surface that has not consistently suited the game — a key area of opportunity on the calendar.

At Grand Slam level (Roland Garros): Jan Kukal is 4–5 (44.4%) across 9 Grand Slam matches — below .500, though the elite draw depth at the Slams makes that a notoriously difficult barrier to crack.

5 quarterfinals on clay, including one run to the semifinal — regularly reaching that stage is a solid baseline, with the next step being to break through to the final rounds more often.

By format on clay — best-of-five: 14–15 (48.3%); best-of-three: 17–24 (41.5%). Slightly better in five-set matches on clay — a positive sign for the Slams specifically.

Best season: 1969 — 10–6 (62.5%) from 16 matches. The best single-season display to date — a useful reference point as the clay record continues to develop.