Ironman and 70.3 finish time.

Put in paces you have actually held for the distance, not your best 20-minute numbers. The swim pace is your pace from a long open-water or continuous pool swim, in a wetsuit if the race allows one. The bike speed is an average over the whole ride, aid stations and hills included: look at a long training ride on a similar course, not the fastest hour of it. The run pace is what you can hold off the bike, which is slower than a fresh half marathon.

Then use the sub-X solver backwards. Type the finish you want and look at what the bike and run have to be. If the run pace it asks for is faster than you have run off the bike in training, the honest answer is a slower bike: the table shows what each mile per hour on the bike costs on the run. Over-biking is the most common way a long-course race goes wrong, and the slower bike split almost always produces the faster day.

On the day, aim for a negative split on every leg you can. Swim the first 200 metres easy and settle in. Ride the first hour as if you were warming up, eat on schedule, and keep your effort even on hills rather than your speed. Start the run slower than goal pace for the first two or three miles and let the pace come to you. Transitions are free time: practise them, lay your kit out the same way every race, and keep them under the numbers you typed here.