# What a slip costs *Find out how often your customers can buy before you argue about the delivery date* --- A plan only becomes real when it's in numbers people are held to, and in a [[Turnarounds|business you have just taken over]] the budget is where that happens. Expect to send the first cut back. It will arrive with everything still going backwards, and the work is in the assumptions: when development lands, when a deployment becomes something you can sell, and what a missed window costs. That last one is where most plans quietly break. The delivery report says four months late, on budget, amber, recovery plan in place. It says nothing about the calendar the customer is on, and the calendar the customer is on decides almost the whole cost. <iframe src="https://anishshailpatel.github.io/instruments/what-a-slip-costs.html" title="What a four-month slip costs on different buying cycles" width="100%" height="1120" style="width:100%;border:0;display:block;margin:1.2em 0;" loading="lazy" sandbox="allow-scripts allow-same-origin"></iframe> The case is a £1.2m build over nine months, worth £900k a year once the customer base is fully on it, which takes about two years from launch. Judge it over a fixed five years, the way a board will, so a delay pushes benefit off the end rather than adding it on. Then leave the slip at four months and change only how often the customers can buy. On a monthly cycle a four-month slip costs four months of benefit, about £300k of five-year cash, and payback moves from month 36 to month 40. The pack said four months late and for once the pack has it about right. Nothing compounds, because there is never a wait for the next chance to sell. On an annual cycle the same slip costs £900k and pushes payback out by a year. The build is ready in month 13, the window was month 12, and the customers commit in month 24. One month past the window is the whole of it: the other three months of the slip cost nothing at all, because they were absorbed by slack that was already there. On a three-year cycle the same slip costs nothing. The build is ready in month 13 and the next buying moment is month 36, so there are 23 months of slack in hand, which is more than the slider can spend. When it does run out, the window after that is month 72. > [!note]- The working > £900k a year is £75k a month at full adoption, and adoption ramps: 40% of it in the first year on the customer, 75% in the second, full from the third. Against a £1.2m build that means the cumulative line crosses zero at month 36 rather than month 25, which is what the ramp costs you. The instrument runs the same arithmetic and draws the line. ## Why the pack cannot see this The delivery report is measuring the thing it can measure. Months late against a plan is a real number, honestly produced, and it is linear: four months late is twice as bad as two. The cost is not linear at all. It is flat, then a cliff, then flat again, and where the cliff sits has nothing to do with the project team. That asymmetry is worth naming when you build the case rather than when you miss it. In a business that sells on an annual cycle, a missed implementation window doesn't cost a month, it costs a year, and you can't sequence a plan without knowing it. Slide the slip with the cycle set to yearly and watch the line sit perfectly still for three months and then drop. Where renewal dates are spread across the base, the cliff flattens into a slope and this matters much less, which is worth checking before you assume you have a cliff. Where the whole base moves together, and plenty do, it is real. The practical consequence is that two projects with the same slip risk are not the same risk. The one landing three weeks before an annual renewal round deserves the attention, the contingency and the ruthlessness about scope, so you spend your worry where the cliff is rather than spreading it evenly because the RAG report does. ## What to put in the assumptions None of it is the delivery date. You need how often your customers can actually buy, which for most businesses is a real and knowable number: an annual budget round, a school year, a licence renewal, a fleet replacement, a maintenance contract. Then when the next one falls relative to when the build is ready, and how much slack that leaves, in months, so everyone can see how much of it has been spent. The schedule conversation then changes shape. It stops being about whether four months late is acceptable, which nobody can answer, and becomes whether the build still lands inside the window, which everybody can. The right answer to "we've slipped a month" is sometimes that it does not matter, and being able to say that with a number behind it is worth as much as being able to say the opposite. What you send back to the team is the assumptions. The totals follow from those. ---