Quick answer: the best results in a 2007 meta-analysis came from a two-week taper that cut training volume by 41 to 60%, decreasing progressively, while keeping intensity and the number of sessions. From a 40-mile peak with a 50% cut, that means about 28.3 miles in week one and 20 miles in race week.
How to use the taper calculator
Set your race date, type the volume of your biggest regular week (miles or kilometres, the result uses the same unit), choose two or three weeks and how deep to cut. The table gives the dates of each taper week, ending on race day, and the volume to aim for.
What the research found
Bosquet, Montpetit, Arvisais and Mujika (2007) pooled 27 studies on tapering. The largest performance gains came from a taper of about two weeks in which volume was decreased exponentially by 41 to 60%, with no change to training intensity or frequency. In plain terms: run as often as before, keep some faster running, and make the runs shorter.
How the weekly numbers are worked out
"Exponential" means each week drops by the same percentage, not the same number of miles. This calculator reads the cut you choose as the level reached in race week, and spreads it evenly on that curve: week k = peak x (1 - cut)^(k / weeks). That is our way of applying the finding, not a formula from the paper.
Worked example: peak 40 miles, two weeks, 50% cut. Week 1 = 40 x 0.5^(1/2) = 40 x 0.707 = 28.3 miles. Race week = 40 x 0.5 = 20 miles. For a marathon or half marathon, our choice is to apply the race-week figure to the days before the race and not count the race itself: a marathon alone is 26.2 miles, more than the whole race-week figure at a 50% cut from any peak under 52.4 miles. The taper guide works through both readings. Over three weeks the same cut gives 31.7, 25.2 and 20 miles.
Two or three weeks?
The meta-analysis points to about two weeks. Some marathon plans use three; the calculator offers it so you can compare, with the same overall cut spread over more days. If you are unsure, the shorter, middle option keeps you closest to what the studies tested.
Limits
The studies mixed sports and levels, and a taper cannot add fitness you did not build. Keep easy runs easy, sleep, and do not try new shoes or foods in the last week.
Plan the race itself with the marathon pace chart, load up with the carb loading calculator and plan gels with the race fueling calculator.
Sources: Bosquet, Montpetit, Arvisais and Mujika (2007), Effects of tapering on performance: a meta-analysis, Med Sci Sports Exerc. Rules checked . Found a problem? Tell us.
Questions
How long should a marathon taper be?
The 2007 meta-analysis by Bosquet and colleagues found the best results with about two weeks. The calculator also offers three weeks so you can compare.
How much should I cut mileage during a taper?
The studies point to a 41 to 60% cut in volume, made progressively. From a 40-mile peak, a 50% cut takes race week to 20 miles.
Should I still do speed work while tapering?
Yes, in shorter doses. The best tapers in the analysis kept training intensity and the number of sessions the same and cut only the volume.
Why do I feel sluggish during my taper?
Less running changes how your week feels. Keep the number of runs the same and some race-pace work in, which also keeps your legs used to the pace.