Missing one run in a marathon training plan is not a disaster. It happens to almost every runner at some point, and the way you respond matters far more than the missed session itself.
The first mistake is trying to squeeze the run back in at all costs. That often means moving sessions closer together, removing a recovery day or stacking two demanding runs back to back. In most cases, that creates more risk than benefit.
Instead, look at why you missed the session and what is coming next. If it was an easy run and the rest of your week is on track, you can usually let it go. You do not need to make up every easy kilometre. Consistency across the whole training block matters more than one session.
If you missed a harder workout, like intervals, hills or a tempo run, ask whether there is enough space to move it without compromising your next key session. If moving it means you would be doing a hard run the day before a long run, it is normally better to skip it and continue with the plan.
You also need to consider why you missed the run in the first place. If it was because of work, travel or life getting in the way, you may feel completely fine the next day. If it was because you were exhausted, sick or unusually sore, trying to make the session up immediately may be the wrong decision.
Marathon training works because of the accumulation of weeks and months of training. Fitness is not lost because of one missed run. In fact, one extra recovery day can sometimes leave you better prepared for the next important session.
The runners who tend to run into trouble are often the ones who try to protect the plan instead of protecting the training process. They chase missed mileage, add extra sessions and end up carrying more fatigue into the following week.
A better approach is to keep your priorities clear. Protect your long runs and your key quality sessions where possible. Keep enough recovery between demanding days. Do not add mileage simply because the calendar says you missed it.
If you miss several runs in a row, that is different. At that point, jumping straight back into the original plan may be too aggressive. You may need a few easier days or a gradual return before continuing with the planned workload.
The aim is not to complete 100 percent of a training plan. The aim is to arrive at race day fit, healthy and ready to run. Sometimes the smartest thing you can do is accept the missed run and move on.