The number on the box is not the bandwidth you get

The gap between the last two columns is the line code, and it is the single most misleading thing about the headline numbers. Note that HDMI 2.1's 48 Gb/s and DisplayPort UHBR10's 40 Gb/s deliver 42.7 and 38.8 — much closer together than the raw figures suggest.

• DVI single link — Capped by a 165 MHz pixel clock, which is where the 1920×1200 limit comes from. DVI-I adds analogue pins that carry VGA and nothing digital.
• DVI dual link — A second set of TMDS pairs in the same shell. The connector looks nearly identical and a single-link cable in a dual-link socket simply loses the top half of the bandwidth.
• HDMI 1.0–1.2 — Electrically DVI single link with audio and CEC added. This is why passive DVI–HDMI adapters work and passive DisplayPort ones do not.
• HDMI 1.3–1.4b — 340 MHz pixel clock. 1.4 added the 4K modes at 30 Hz and the Ethernet channel almost nothing ever implemented.
• HDMI 2.0–2.0b — The last TMDS generation, and sized almost exactly for 2160p60 at 8-bit. One bit of extra colour depth does not fit, which is the origin of a great deal of 4:2:2 subsampling.
• HDMI 2.1–2.1b — A different signalling scheme entirely — Fixed Rate Link, four lanes instead of three, and a clock recovered from the data rather than sent alongside it.
• HDMI 2.2 — FRL again, at twice the lane rate, with its own new cable certification. Displays that need it are still rare.
• DP 1.1 (HBR) — DisplayPort is packetised rather than a raster clocked down a wire, which is what lets one link drive several displays.
• DP 1.2 (HBR2) — Carries 2160p60 at 8-bit three years before HDMI could, which is why professional video kit went DisplayPort first.
• DP 1.4 (HBR3) — The last 8b/10b rate, and still the most common on installed graphics cards. Display Stream Compression arrives here and does most of the heavy lifting above 4K.
• DP 2.1 UHBR10 — The new line code matters more than the rate: 128b/132b wastes 3% where 8b/10b wasted 20%.
• DP 2.1 UHBR13.5 — The middle tier, and the one most likely to be what a "DisplayPort 2.1" port actually negotiates.
• DP 2.1 UHBR20 — The headline number. A source, a display and a certified DP80 cable are all required, and a port advertising 2.1 need implement none of it.

The small figure is headroom in Gb/s — how much payload is left over, or how much is missing. A row that clears a format by a fraction of a gigabit is one colour depth or one refresh step away from not clearing it.

Two cells look wrong and are not. DVI single link and HDMI 1.0–1.2 fail 1080p60 here by half a gigabit, because this table is at 10-bit and both are 8-bit interfaces in practice — at 8-bit they clear it with room to spare, which is why everyone remembers them managing it. DisplayPort HBR2 misses 2160p60 by the same hair for the same reason: it carries 4K60 at 8-bit and not at 10.

This calculator needs JavaScript. Without it, the table above still gives six common formats at 10-bit.

The interfaces and their payload rates come from the same array the table above is built from, so the two cannot disagree. What the calculator adds is a pixel clock for formats nobody standardised: it uses the CTA-861 timing where one exists and CVT reduced blanking otherwise, and tells you which. The difference is real — 1080p60 is 148.5 MHz as a television format and about 138.7 MHz as a computer one, because they blank differently.