Duckworth-Lewis-Stern Method: How Rain Rules Work in Cricket

The Duckworth-Lewis-Stern method — originally the Duckworth-Lewis method before Steven Stern updated it in 2014 — is a mathematical formula used to calculate revised run targets in limited-overs cricket matches interrupted by rain or bad weather. Before its introduction in 1997, rain interruptions were handled by cruder methods — typically the average scoring rate method or the highest-scoring overs method — that produced manifestly unfair outcomes. D/L solved most of these fairness issues through a resource-based model, though it has its own complexities and remains controversial in some applications.

The Resource-Based Concept

The DLS method is based on the concept that a batting team has two 'resources' available — wickets in hand and overs remaining. The combination of these two resources determines how many runs a team might be expected to score. A team that has used no wickets with 50 overs remaining has the maximum resource percentage (100%). As overs are used and wickets fall, the resource percentage decreases. The DLS method calculates how much resource percentage is lost when overs are removed by rain and adjusts the target accordingly.

The formula ensures that if rain removes overs from the team currently batting second (chasing), their target is reduced proportionally to the reduction in resource percentage. If rain interrupts the first innings, the first team's notional final total is recalculated based on how many resources they used before the interruption. The system is therefore applicable to interruptions at any point in any innings — not just straightforward 'shorten the match by 5 overs' situations.

The Historic Pre-D/L Methods and Their Failures

Before DLS, the most common rain rule was the 'average run rate' method — dividing the first team's total by their overs faced and setting a proportional target. This was fatally flawed because it assumed scoring was linear throughout an innings, when in reality teams accelerate significantly in the final overs. A team scoring at 4 runs per over for 40 overs is not expected to score at 4 for 50 overs — the final ten overs typically produce 6-8 per over.

The 1992 World Cup semi-final between South Africa and England became the most infamous pre-D/L failure. South Africa needed 22 from one ball — a mathematically impossible target created by removing overs from South Africa's chase. The method's failure in this high-profile situation accelerated the push for a better solution. Mathematicians Frank Duckworth and Tony Lewis developed their resource-based system in response to exactly these kinds of problems.

Famous D/L Controversies

D/L has not eliminated controversy. The 2003 Cricket World Cup South Africa exit (described in a separate article) resulted directly from a misunderstanding of the DLS target. More generally, the method has been criticised for being difficult to compute without a spreadsheet or special calculator, making it inaccessible to players and spectators in real time. When play resumes after a rain break and players are given revised targets, both teams must trust the match officials' calculations — a trust that has occasionally been misplaced.

Steven Stern's 2014 revision improved the method's accuracy in high-scoring T20 and ODI matches, where the original D/L underestimated the value of the final overs' resources relative to what modern batters can score. The Professional Edition is now the ICC's official version. Applications of D/L to T20 matches — where interruptions can reduce a match to as few as 5 overs — have produced some unusual targets that still generate debate.

When D/L Cannot Be Applied

The DLS method requires a minimum number of overs to be bowled before a result can be declared. In ODI cricket, each team must face at least 20 overs (in a 50-over match) for a D/L result to be valid. In T20 cricket, at least 5 overs per side must be bowled. If rain prevents even the minimum overs being bowled, the match is abandoned with no result. This minimum-overs requirement was itself controversial — matches shortened to 20 overs from 50 use the DLS target but the statistical representativeness of such a short match has been debated.