When youre training for a race, a good training plan is key. With that training program, youll have all your runs planned out for you, with just the right mix of long runs, speed work, and easy mileage to get you to the start line strong and ready. But what do you do when the plan doesnt match up with your life? You get sick and miss a week, or you realize too late you started on the wrong date. Or maybe the plan calls for something you just cant make happen on schedule, like a tune-up race.What do I do??? I hear you wailing. Well, dont worry. Ill tell you what you do: you do your best to follow the plan without letting any feelings of guilt or nervousness take over. Missed workouts are in the past, and youll move on without trying to make them up. For the most part, anyway. Lets look at a few scenarios where you might have questions. But firstlets zoom out so we can see the big picture.Understand what your training plan is trying to doBefore we can talk about whether to do this or that run off-schedule, we need to get our bearings and understand what each part of the training plan is trying to do. Im going to describe the phases in a typical marathon training program, which will apply to most hard training programs, including those for half marathons.There are a few different phases over the course of what's usually a 12- to 18-week plan, and they're laid out something like this:The beginning, or baseWhat it is: Several weeks where you run a similar number of miles per week to what you were used to doing before you started this program. During this on-ramp phase, the program will challenge you to keep a consistent training routine and add some extra distance to your long runs and perhaps some extra speed work or strength training that you had previously been neglecting. This may or may not feel like its own phase; it may just be the beginning of the build.(On the flip side, it's possible to have several months of base building before your plan transitions you into the build. This is common if you're using a long term plan, like the kind you get from an app or wearable like a Garmin if you put in a race date that is far in the future.) How youll feel: Youll feel pretty good during this phase.Your biggest priority in this phase: Sticking to the program and preparing for the work to come.The buildWhat it is: A nice long stretch focused on building up your mileage, both in the length of the long run and in total weekly mileage. This is the longest phase of the program, perhaps six to eight weeks long.How youll feel: Youll experience some fatigue, sore muscles, and maybe some blisters or minor injuriesbut these tend to be pretty mild and overall youre feeling OK.Your biggest priority in this phase: Keeping up with the increases and taking care of your body (good nutrition, shoes, etc.) so that you can stay healthy and keep training.The peakWhat it is: This is the three to four weeks or so when mileage is highest, workouts are hardest, and the fatigue is really starting to catch up with you. If its a marathon program, youre probably doing some 18+ mile long runs. If your race is a half marathon or less, you may be doing long runs that are longer than your race.How youll feel: Somewhere between pretty rough, but hanging in there and frankly, I feel like shit.Your biggest priority in this phase: Surviving.The taperWhat it is: After all that hard work, you finally get a break. The long runs are suddenly a lot shorter, and youll find yourself running a lot less mileage than you were during the peak. This phase is often about three weeks long for a marathon, and one to two weeks for a half marathon. For shorter races it may be just a few easy days so you can rest up before race day.How youll feel: Often this is when you feel the worst, because all of that fatigue has built up, but you havent had enough of a break yet to feel rested. Its also very normal to go a little crazy as you start wondering whether your training was really good enough and whether youre really ready for your race. But this is all part of the plan, and if you stick with it youll feel like a million bucks on race day.Your biggest priority in this phase: Recovery. Or to put it another way: following the damn program, and not giving in to the temptation to go run an extra 20-miler or a race-pace workout just to be sure that you can.General rules for modifying your training program when life intervenesWith those phases in mind, it becomes a lot easier to figure out what to do when something messes with your schedule. Here are some very general rules to follow in every phase:Its OK to rearrange workouts within a week. For example, if you cant do your long run on Saturday, go ahead and move it to Friday or Sunday.(Get in the habit of looking at your schedule at the beginning of each week so you can plan ahead.)Prioritize your key workouts (long runs, speed work) and try not to miss those. If you have to miss a run for scheduling/life reasons, make the one you drop an easy run.Dont try to make up missed runs, especially if you were sick and/or had to miss multiple sessions. Pick up where you left off. And give yourself some grace those first few days backtake it easy and do what you can.Make sure the program ends on race day. The taper works genuine magic if you time it right, and the peak is what sets up the taper. Dont mess with the timing of those last few weeks.Nobodys perfect. If you manage to do 90% of the program as written, youre still 100% on track and youll do great at the race.Got it? Now lets tackle some specific questions. These are all taken from running forums, subreddits, and coaches anecdotes about what questions they get most often.A coach or experienced friend is the best resource, since they know you and you can discuss the specifics of your situation, but if you're just looking for general advice, here goes:How bad is it to miss a run on your training program? Look, there's a reason your training program lasts 12 weeks or whatever. It's because no single run is going to prepare you for a marathon. That also means no single run is going to ruin your fitness just because you missed it. It is OK to miss a run sometimes. If it's one of your short or easy runs, your fitness won't really suffer at all. Even if it's a long run or an important workout, it's not the end of the world to miss one or two of those. Think of the runs as like money you're putting into a piggy bank. If you aim to put in $5 a week, and you miss putting in a penny here or there, it's not a big deal. But if you're consistently totaling $4 rather than $5, you'll come up short in the end. It's more important to be consistent than to worry about one day's individual contribution. Sometimes you're missing a run for a good reason, anyway. You got sick and now you're recovering. Or you had a vacation and you took some time off and enjoyed yourself for once. The benefit of missing that run is arguably more valuable than the training you would have gotten by doing it. I started the program too early, and now I have extra time to fill. Should I repeat some of the weeks?That depends on where you are in the program. Do not repeat weeks in the taper. Thats meant to be a short, sharp decrease in mileage. Stretching it out will rob it of its power. (Tapers are magic, I swear.)You also do not want to repeat hard weeks in the peak. Remember, thats the highest fatigue part of the program, and youre just trying to hang in there and not let it kill you. If the program is designed to have one 20-mile training run, it is foolishness to try to run two in a row.(There are, of course, exceptions to these rules. Some people might benefit from a longer taper, or have the fitness to do an extra long run and recover from it without too much trouble. But Im trying to keep my advice general, and most people who say fuck it, Ill do an extra long run will end up regretting it.)So what can you do? Id recommend these approaches, in this order of preference:Extend the beginning or build phases. You can certainly repeat week five of a 16-week program, no sweat. Feel free to make the repeated week(s) slightly different, maybe decreasing the long run by a mile or two, or doing hills instead of track repeats. Just try to keep it within the spirit of what that phase of training is trying to accomplish. Add cutback weeks during the peak or late build phases. If youre already in the peak phase when you notice your scheduling mishap, add an easy week in between some of the hard weeks. For example, the Level 3 Boston Marathon program has a 17-20 mile run in week 16, followed by 18-20 in week 17. You could insert a week in between where your long run is 13 miles or so to give you a little bit of a break. Or say youre following a Hal Higdon program that alternates between 20-mile and 12-mile long runs during the peak. Add an extra repeat of that cycle, maybe doing 16 or 18 rather than another 20-miler (since multiple 20s is a lot), and following it with a 12 according to the pattern.When in doubt, make the added week easier than the weeks before and after it. Your body will appreciate the extra recovery.What if I dont have a tune-up race to run?Some training plans will throw in a race partway through the program. (Our resident marathoner Meredith Dietz explains the rationale here.) A marathon program might have you race a half marathon in the middle of your training. A half marathon might have you race a 10K.Ideally, this will be an actual race. Youll sign up for the My Town 10K and have to figure out all your race day logistics: how early to wake up, what to eat, whether you want to carry your phone, and so on. Youll also have the pressure of a timed course (no free pauses for water breaks) and the adrenaline rush of a crowd cheering you on.Having to deal with all that bullshit is half the point of doing a tune-up race. The other half is getting a chance to see how fast you can really run, and then you can use that result to help you decide what pace to target for your big race. (Plug in your race time here to see your predicted times at other distances.) But maybe there isnt a 10K in your town that weekend. Here are, in my opinion, your best options:Find a race of the correct (or similar) distance on a different weekend. Usually this isnt a part of the training program where the timing is super critical. If you can get the full race day experience a week or two earlier or later, go ahead and swap things around to make that happen.Run a time trial. This is just a race that you do on your own. There wont be a crowd or a bib pickup table, but you can still test your fitness over the programmed distance. Reward yourself with a stale post-race bagel for verisimilitude.Just do a regular long run. Usually the tune-up race takes the place of your weekend long run. Look at the weeks before and after it on the calendar, and ask yourself if there wasnt a race here, what would it be instead? Make your best guess, and then do that.What if I want to add a race that's not on the program?This is the opposite of the dilemma above. There isnt a race scheduled, but you want to do one anyway. Your friend is running a 5K and you'd like to join them, or some other scenario where youll be running, but not hitting the programmed distance.The simplest answer is just: run a loooong warmup and cooldown. Three real easy miles before the 5K shouldnt ruin the race for you; in fact, youll probably feel nicely warmed up by the time you get to the start line. And then you can do the other six miles as an extended cooldown.Same idea if youre meeting a friend for a run. If they want to do a nice easy five-miler, you can do seven before they show up, run your last five with them, and then go to brunch together.If the race is a longer onesay, a 10Kyou can also just treat it as a tune-up race. Run it all-out, and dont bother making up the mileage. Depending on where you are in the program, a race and a long run might be too much to recover from.You wouldnt want to do this every week, but once or twice in your training plan isnt the end of the world.I missed my longest run, and now its taper time! Should I squeeze in a 20-miler real quick?You know the answer to this one by now: no. The taper is for recovery. Also, my god, you have no idea how many people miss their last 20-miler and then do absolutely fine at their marathon.I ran all my long runs, but some of them went really badly. I think I can redo my last 16-miler, but do it better this time. How do IThat's the neat thing, you don't. What if I am a special snowflake and believe these rules dont apply to me?Honestly: maybe youre right.A cookie-cutter program is not guaranteed to be perfect for everyone. Just promise me something: whatever bad decisions you make, learn from them. Maybe you think youll be fine with a shorter taper. If you truly want to test that hypothesis, shorten your taper! Keep notes. And then see how you do in the race.Just remember that this kind of self-experimentation works best if you do the program as written your first time around, and then tweak it when you run your next race. Youre learning how you respond to training, which is an incredibly valuable skill as you grow as an athlete.