Our tools raise the game by giving users the option to run the calculation over a period starting from any upcoming month. 

Communicating this in the interface is a fun challenge. In the example above the period, which is a 3 year contract hire agreement, starts in Jan 2015 meaning only 3 months of the hire period lands inside tax year 2014/15. To illustrate this the grey bar has 4 year-segments, each representing a tax year. Below the first year-segment is an indication bar with the right quarter shaded dark to represent it being partially filled. The indication bar below the centre 2 segments are entirely full indicating that the contract hire occupies the entire year and the fourth year-segment has the left three quarters darkened to show that only the first 9 months are occupied. The red shading shows which tax year is currently being displayed in the table below. Clicking any of the segments will switch the table to a different tax year. 

We pored over several alternatives before settling on this interface design. The familiar design of a timeline with horizontal bars spanning overlapping periods is easily comprehended throughout society. The flow of time being represented as moving from left to right is natural in western languages. Darker colours representing mass and lighter ones being empty is ingrained in all of us from years of using mobile phone battery charge indicators. 

So when you approach a new build of a tool and gather the sum of your knowledge together, a designer doesn't really have a choice! They are merely collaborators who work with a recipe of circumstances to produce the best solution they can.