The 2021 Giro d'Italia will be the 104th edition of the Giro d'Italia, one of cycling's Grand Tours. The Giro began in Turin with an individual time trial on 8 May, and Stage 12 occurred on 20 May with a stage from Siena. The race finished in Milan on 30 May.

Classification standings Legend Denotes the leader of the general classification Denotes the leader of the mountains classification Denotes the leader of the points classification Denotes the leader of the young rider classification

Stage 12 20 May 2021 — Siena to Bagno di Romagna,

Following the previous day's fireworks to Montalcino, the riders tackled another hilly course from Siena to Bagno di Romagna. At , the distance tied the second longest stage of this year's race. There were a few hills during the first part of the stage before the riders passed through the first intermediate sprint after . Immediately afterwards, the riders climbed the third-category climb of Monte Morello. There were also two consecutive second-category climbs before the riders climbed the third-category Passo del Carnaio. The finish featured a descent of before a flat run-in to the finish line.

At the start of the stage, there was a crash at the back of the peloton. One of the riders involved was Marc Soler (), lying in 11th overall in GC. He tried to chase back but he eventually had to abandon the race due to back pain. A few kilometres later, there was a serious crash involving former race leader, Alessandro De Marchi (), forcing his abandonment from the race. Following the stage, he was diagnosed with a broken right collarbone, six broken ribs, and broken first and second thoracic vertebra. At the front of the race, several riders tried to attack from the peloton but for the first , no attack would stick. Eventually, a 16-rider break broke clear of the peloton. Nicolas Edet () and Giovanni Visconti () soon bridged over to the break to make it 18 riders out front. Mountains classification leader, Geoffrey Bouchard () was among the riders in the break, while the best-placed rider was George Bennett (), at around 21 minutes down. As such, the break was allowed to stay away, with the peloton allowing them to get a maximum advantage of around 13 minutes.

As the break reached the first intermediate sprint, Belgian national champion Dries De Bondt () took maximum points while Bouchard took maximum points at each of the stage's first three climbs. As a result, Bouchard increased his total in the mountains classification to 96 points, double the total of the second-placed Egan Bernal (). The break continued to work together until the final climb of the day, the Passo del Carnaio. Gianluca Brambilla () kicked off the attacks at the front but it was Andrea Vendrame (AG2R Citroën Team) who was able to get a gap on the steepest section of the climb. Eventually, Bennett, Brambilla, and Chris Hamilton () joined Vendrame at the front. The four riders were together over the top of the climb until the descent. With to go, Hamilton attacked his companions, with Vendrame joining him at the front. Bennett and Brambilla were distanced by the attack as they argued and refused to work together. During the sprint for the line, Vendrame proved to be the faster sprinter as he took the stage win.

In the maglia rosa group, Ineos-Grenadiers continued to control the peloton. They rode at a steady pace until the Trek-Segafredo duo of Giulio Ciccone and Vincenzo Nibali attacked on the final climb. Although they would be caught, Nibali continued his attack on the descent. While trying to chase him, Gianni Moscon (Ineos-Grenadiers) slid on a corner but he would get back on the bike and finish the stage. Nibali eventually took 7 seconds on the finish, while most of the contenders finished more than 10 minutes behind Vendrame.

Stage 13 21 May 2021 — Ravenna to Verona,

The thirteenth stage featured a pan-flat course from Ravenna to Verona. There was an intermediate sprint after , while the sprint for bonus seconds occurred after . There were no hills or climbs on the route, with the stage representing one of the final chances for the pure sprinters in this year's race.

As soon as the flag dropped, two riders, Samuele Rivi () and Umberto Marengo (), immediately attacked from the peloton. Shortly afterwards, Simon Pellaud () joined the duo at the front, representing the final breakaway of the day. The trio was allowed to gain a maximum advantage of around seven and a half minutes before the sprinters' teams kept the break in check. Soon after the first intermediate sprint, tensions arose with the three out front and soon afterwards, the three riders attacked each other. This caused their advantage over the peloton to quickly decrease. While the peloton remained relatively quiet for the majority of the stage, Rémi Cavagna () sensed the possibility of crosswinds with around to go. He was quickly chased down and the peloton eased up once again. The peloton continued to eat into the breakaway's advantage but avoided catching the trio immediately. Eventually, with around to go, the catch was made and the sprinters' teams started to bring their sprinters to the front. Going into the final kilometre, led the peloton to set up their sprinter, Peter Sagan. However, with around 500 metres to go, Edoardo Affini () made a late attack and immediately gaining a few seconds of an advantage. Fernando Gaviria () started his sprint first, despite having lost his saddle on the approach to the line. Giacomo Nizzolo () went to his slipstream, passing Gaviria and Affini to take the stage win. This marked Nizzolo's first Grand Tour stage win, having previously finished second on a stage for a total of 11 times. Affini held on for second while Sagan finished third to keep his lead in the points classification. All of the contenders finished safely in the peloton, ahead of the crucial mountain stage to Monte Zoncolan.

Stage 14 22 May 2021 — Cittadella to Monte Zoncolan,

The race went into the high mountains on the fourteenth stage, with the rider tackling the climb of Monte Zoncolan. The first of the stage are mostly flat, with the exception of the fourth-category climb of Castello di Caneva after . Afterwards, the riders climbed the second-category Forcella Monte Rest. The climb is long with an average of 5.9 per cent. Following the descent, the riders went through a valley before making their way towards the base of the climb of Monte Zoncolan. This marked the seventh time that the Giro tackled the climb. Unlike the previous five passages, the riders took on the climb from the Sutrio side for the first time since the climb made its Giro debut in 2003. From Sutrio, the climb is long with an average gradient of 8.5 per cent. The first averaged 8.3 per cent before easing for the next kilometre or so. The last of the climb averaged 13 per cent, including pitches of 27 per cent towards the top. In addition, the riders had to deal with fog and small visibility towards the summit of the climb.

For the first part of the stage, several riders tried to attack from the peloton until an 11-man group broke clear. The break was allowed to gain a maximum advantage of around eight and a half minutes before the peloton started chasing. However, Edoardo Affini () and Jacopo Mosca () mainly shared the workload in support of fellow breakaway companions, George Bennett and Bauke Mollema, respectively. As a result, the break maintained their advantage and reached the base of the final climb with a lead of six minutes over the peloton. At the bottom of the climb, Jan Tratnik () got a gap over his breakaway companions. No one immediately reacted to his move until Lorenzo Fortunato () attacked the rest of the chasers. Fortunato eventually bridged over to Tratnik and the pair worked together to increase their advantage. From the chasing group, Alessandro Covi () attacked in an attempt to bridge over to the duo out front but he would not get closer than 40 seconds. With to go, Fortunato dropped Tratnik on the steep portion of the climb. Although he was within Tratnik's sight for the rest of the stage, Fortunato maintained his gap to take his first professional victory. Tratnik finished 26 seconds behind while Covi finished almost a minute down.

From the maglia rosa group, paced the group for the majority of the stage in support of their leader, Aleksandr Vlasov. On the descent of Forcella Monte Rest, the peloton split into three groups, with Vlasov and Egan Bernal () making it in the first group. and chased in the second group while Remco Evenepoel and chased from the third group. Eventually, the catch was made in the valley before the final climb. Astana continued to pace the peloton on the bottom of the Zoncolan before Ineos-Grenadiers took over with around to go. The first contender to lose touch with the group was Vincenzo Nibali (Trek-Segafredo), who was dropped with around to go. Evenepoel also struggled to follow the pace and was dropped with around to go. Ineos continued to whittle down the group until Simon Yates delivered his first attack with to go. The only rider to go with him was the race leader, Bernal, while the group continued to splinter behind. The pair caught the remnants of the breakaway until Bernal attacked Yates inside the final kilometre. Bernal finished fourth on the stage, with Yates losing 11 seconds. A trio consisting of Daniel Martinez (Ineos-Grenadiers), Damiano Caruso (Team Bahrain Victorious), and Giulio Ciccone (Trek-Segafredo) finished 39 seconds behind Bernal. Emanuel Buchmann () and Hugh Carthy (EF Education–Nippo) lost 46 and 54 seconds, respectively. Despite the work of his team, Vlasov struggled inside the final 3 kilometres and lost more than a minute while Evenepoel shipped more than a minute and a half.

In terms of the GC, Bernal increased his advantage to more than a minute and a half over the second place, now occupied by Yates. Caruso maintained his third place, but he was now 1' 51" behind while Vlasov dropped to fourth at 1' 57" behind. Carthy and Buchmann were now over two minutes down with Ciccone more than three minutes down. Evenepoel dropped to eighth at almost four minutes behind Bernal.

Stage 15

23 May 2021 — Grado to Gorizia,

The fifteenth stage took the riders on a hilly course from Grado to Gorizia. The first were mostly flat with an uncategorized climb after and an intermediate sprint after . Afterwards, the riders entered Slovenia before tackling three laps of a circuit, with the circuit consisting of the fourth-category climb of Gornje Cerovo. Following the third passage of the climb, the riders deviated from the circuit before reaching the second intermediate sprint at Nova Gorica with to go. Immediately afterwards, there was a short steep ramp before reaching the finish at Gorizia.