Buffer time is insurance, and like any insurance the right amount depends on what the loss would be rather than on how likely it is. Here are ten considerations that decide it. Here are ten.
1. The Cost of Being Late Is Not the Cost of Being Early
Arriving early costs you time you spend waiting. Arriving late can cost the whole journey, the money paid for it and everything arranged at the other end – and those are not comparable quantities.
The asymmetry is the whole calculation. Unequal consequences are why the sensible margin is larger than the average delay.
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2. So Work From the Consequence Rather Than the Average
A journey where a miss means a two-hour wait for the next one justifies a small margin; one where a miss means a lost day and a new booking justifies a large one.
The likelihood matters less than the outcome. Consequence-led buffering is the method almost nobody applies.
3. Frequency Changes Everything
A service running every ten minutes needs almost no margin, because missing one costs ten minutes; a service running twice a day needs a great deal.
It is the single largest variable. Service frequency is what should set the buffer and rarely does.
4. The Variable Part Is Rarely the Journey
Delay accumulates in the parts nobody plans – getting out of the house, finding parking, queues, the walk from where you arrive to where you need to be – rather than in the travelling itself.
The journey time is the reliable part. Unplanned segments are where the margin actually gets consumed.
5. Count the Transitions, Not the Distance
Each change from one thing to another – vehicle to foot, building to building, one service to another – is a point where time can be lost, and the number of them predicts the risk better than the total distance.
Two changes are worse than twice the distance. Transition count is the better predictor of delay.
6. Early Is Only Painful If There Is Nothing to Do
A margin spent somewhere with a seat, a drink and something to read costs very little; the same margin spent standing outside a locked door is truly unpleasant.
That difference is under your control. Quality of the wait is what makes a large buffer tolerable.
7. So Build the Buffer Where It Is Comfortable
Arriving early at the place with facilities and leaving the uncomfortable stretch until last converts waiting time into something usable.
It is the same total time arranged differently. Buffer placement matters as much as buffer size.
8. The Calculation Is Not the Same for Everybody
Anybody who cannot move quickly, is travelling with others who cannot, or is carrying more than they can manage in a hurry needs a substantially larger margin, because the recovery options that make a small buffer survivable are not available.
A rushed transfer is not a universal fallback. Individual circumstances change the answer entirely.
9. Other People Set Their Own Margins
Travelling with somebody whose instinct differs is a recurring source of friction, and the disagreement is about risk tolerance rather than about time.
Naming that resolves it faster than arguing about minutes. Differing tolerances are what the argument is actually about.
10. Pick the Number Once and Stop Recalculating
Deciding a margin in advance and treating it as fixed removes a decision from a morning that has no room for one, and prevents the gradual erosion that happens when it is reconsidered each time.
Every recalculation shaves a few minutes off. A fixed rule is the protection against your own optimism.
Insurance Priced by the Loss, Not the Odds
An asymmetry between being early and being late, a frequency that should set the margin, transitions rather than distance predicting delay, and a buffer placed where it is comfortable to spend.
The eighth item is worth restating because most advice on this ignores it. The whole idea of a small margin assumes that if something goes wrong you can move fast – and that assumption does not hold for everybody, or for anybody travelling with people it does not hold for. Where it does not apply, the sensible margin is substantially larger and nobody should feel odd about it.
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