McDonald has been running halves for the past 30 years.
He finished his first half-marathon, an off-road run in Hanmer Springs in 1984, in a time of 1hr 43min and from there he has never looked back.
"I really enjoy the challenge of completing them - plus the social aspect of running with my wife and other competitors."
His best time came at the Christchurch Half Marathon in the mid-1980s when he completed the run in 1hr 20min; his worst time was at the Rotorua 3D Half-Marathon in 2hr 39min - "Not that finishing any half-marathon should be considered 'worst."'
On April 12, McDonald and his wife Julie will complete their 10th Xterra Half-Marathon.
"This is by far my favourite half in New Zealand because of the fantastic scenery, it is a well-organised event and there are great people competing and completing the event."
He says all of the halves he has completed over the past three decades have been great in their own way, with many of them challenging, hilly and muddy, and great courses that have offered great scenery.
The goal of reaching the special milestone of 100 halves came to mind three years ago when he competed in the Taupo 63.3 Half-Marathon series.
McDonald completed three halves in three months and he sat back and reflected on his running achievements. "That was when I went back through the diary, added up all the halves I have done and set the goal to complete 100."
The down-to-earth Auckland runner says the half-marathon distance is great because it is achievable for athletes of all abilities. "With a little training and a goal, it can be done."
He recommends people looking to take on a half-marathon run three times a week, with one being a longer run. He says he recovers quicker and stays injury-free for longer with half-marathon training and running, whereas with marathons (he has completed six) he suffers more.
"I still find halves a challenge, but love taking up the challenge. Running allows me to clear my head and sweat like crazy. It also enables Julie and I to keep fit together and compete together ... the couples who run together stay together."
He says running on the roads is tough on the body so over the past 10 years he has moved to off-road training runs and events in places such as Totara Park, the Hunua Ranges, Waiuku Forest, Rotorua Forest and on the Taupo trails.
McDonald believes this has allowed his body to survive the rigours of regular running, and made training and events more interesting and challenging.
"A sensible diet, hydration, massage and good recovery have been the key factors that have prolonged my running career."
McDonald isn't going to stop at 100. In May, he and his wife will run their seventh marathon at the Rotorua Marathon.
It is the 50th anniversary of the event, McDonald's 50th year and the couple's fifth Rotorua Marathon together.
"I want to continue running halves for as long as the body and mind allow. I am always looking for new events to achieve and set goals for ... you must always have a goal."
