Why should you give buffer to project estimation

“Why is this enhancement needs 1 month? Can’t it be done with just 3 weeks?”

This is often being said by project managers to developers. They like to squeeze estimations as short as possible, then in the end wonder why the project is going late. Overtime happens, code quality reduced, bugs everywhere during development until launching. This is one factor that I, as a developer, see as an “incapable” project manager. Furthermore, client often has the same vision: to reduce the estimation as short as possible. Little did they know that having buffer to estimation can bring many benefits rather than shorter one.

Less overtime

Overtime is unproductive. It has been researched many times, and you can easily looking for those in internet or forums. It is obvious, having more buffer to estimation will lead to less overtime needed, in which overall will prevent productivity dropped in long time.

More often than not, I find that unjustified overtime won’t bring better result in a week / month time span, compared to working normally. That’s because usually the task done in overtime is either wrong, bad quality, or incorrect by requirement, in which usually they will be fixed in next week / month.

On the other hand, justified overtime is a necessity, like when there is a critical bug in production, or when a bug is found at last time before launching.

No spare time for changes

Client is very bad at giving requirement. They don’t know what solution they want. They maybe even don’t know what problem they are facing. In my experience, it is 100% chance that at least one small requirement change and at least 50% chance of one medium / big requirement change will happen during project timeline.

Up to this day, prototyping is very useful, especially in programming world. Usually prototype are made to give client a clear picture of how the program will work and how it will help solve their problem. Requirement change are highly possible to happen at this point.

Setting up tight estimation will be a disaster during this time. With tight estimation, any change can’t be integrated in timeline, since everything has already calculated. This can only lead to bad things: late deadline, non-applicable requirement or bad quality.

No room for mistake

Mistake happen, there is no single software in this world that is bug-free. Even the business flow, a requirement that is given by client, may be incorrect. Setting up tight estimation without calculating for mistake and fixing is planning to fail. More buffer to your estimation means the application can be tested more, and more problems can be fixed during the meantime.

You will never deliver “earlier”

There are two situations possible when delivering, that is to deliver “early” or deliver “late”. Deliver “on time” is almost impossible. Usually the project are already done and ready to be delivered at the specific time, so it counts as “early”.

Now which one is better: “longer estimation but deliver ‘early'” or “shorter estimation but deliver ‘late'”. It’s up for personal preference, but usually I find that deliver “early” bring better impression than “late”. “Early” deliver usually being perceived as faster than the opposite, a physiological  things.

Now with setting up tight estimation you are setting yourself to deliver “late” and never “early”.

It is indeed hard at “client” side

Client is hard to deal with. More often than not they aren’t satisfied with estimation given, no matter how tight that estimation is. Though they want tighter estimation, they cannot give clear requirement. “Just make it so that we input this, that and that and it’s saved! How hard is it?” is usually their saying, without knowing what must be done if it needs to be edited if mistakenly inputted, what if there are changed, which system are affected by the change, etc.

That’s why good client will bring good software as well. If you want to teach a client why a tight estimation is bad, give them a tight estimation. Then everytime there are changes and everytime discussion with client about requirement happens, count for all of that. Then after delivery, make an evaluation session with client and present them how all of those things delay the estimation and make the project late.

The delivery time will be the same after all

Many times I find that tight estimation will be late, and the delivery time is usually the same with when I giving buffer to estimation originally. Inexperienced developer and manager usually prefer to give tighter estimation and underestimating how big time will changes and fixing take. The problem is, how much buffer do they need?

In previous job, I like to add 30-50% buffer to my estimation. Then my PM will try to bargain by cutting 20-30%, then give back some buffer to QA and fixing phase. In the end I assume it’s around 25-40% buffer. With that, I usually deliver 10-20% early, so it means 20-40% is a sweet spot, based on how complex and big the project is. It’s just my preference and personal experience, do not take it as guidance, since everyone is estimating differently.

Now if it’s the same after all, why not try to give longer estimation and more flexibility in requirements and development? It will provide better foundation and code quality in software after all.


Give buffer to your estimation. It’s benefit is far outweight the false perception that “shorter estimation is faster”. You won’t be flexible or will having good quality if the estimation is tight.

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