What will happen to the final cost and the duration If the scope of the project changes later in the project?

if a change be required on Project scope or product scope , definitely will has impact on cost and time and even other areas of project and they may decrease or increase. but a professional project manager must have enough authority and ability to analyze the change requests and their impacts and then for major changes get the board acceptance and then after implement  change.

for this situations PM must use their contingencies or managerial reserves for project.

or if it be possible use some techniques like Fast tracking or Crashing for decreasing time.

If scope changes , Cost and Duration both might change due to triple constraints factor But before coming to this conclusion a project manager must do a thorough Impact analysis. If the new change cannot be accommodated with the present cost and schedule then a change request should be raised immediately  to Change Control Board to clear clear approval or rejection. If change is inevitable and there is a budget constraint as well then Proj manager should request Management to release management reserves to achieve the business requirement.

If you are the customer, you can expect that the contractor will present a bill for the extra work.  The "extra cost" depends on how the original price was determined and how the product-to-be-built was specified.  If the specs were loose and non specific, you may be headed for protracted struggle with the contractor over delivery of the original product at the specified price.If you are the developer,  somehow you determined the project COST to you.  You should have accounted for some uncertainty and risk in your PRICE to the customer.  If you didn't, this is a lesson for the future.  But to justify it to the customer, you'll need to compare the original 'deal' and show how & why there is additional work (and cost to you) for the additional features or whatever additions (even subtractions) from the original agreement.  Don't forget to include time for extra design, coding, testing, and staff time for RE-planning and RE-designing things that you've already coded and tested that you might have to deconstruct to include the new requirements.

 Your cost should be mostly, if not exclusively staff hours plus overhead.  You should include any other administrative, supply, travel, software tools, testing tools or other things that were required ONLY for the new requirements.

If the scope changes later in a project, it will certainly have effects on cost and duration. However, if you have already allocated a buffer cost previously, you can utilize that, in case that is enough for the same.

Alternatively, you can discuss with the sponsor for additional budget.

The duration will change too in case of a linear approach. You might require additional time. However, theoretically, if you have some buffer time, or maybe you can execute some activities in a project in parallel to the already in execution activities, you can still complete the project with some marginal additional time which has to be allocated. 

 

In real life, the clients are the biggest hurdle in any project with the fact that their requirement can be an overkill, their expectation and demands may be hard to reach plus they are reluctant to make decisions and answer questions. "All bets are off " must be addressed early in the game and specially when the changes as always after the development phase is already started. With that in mind, your plan as a project manager is to work with changes, keep top management involved or aware of the changes.

 

Please note that "have to Have" and "Nice to have" should be clear at the beginning of the project and as changes take place.

 

Scope , Time , and Cost are main constraints for any project

if any change happened to one of them others will change too .

The fees could be justified by change orders , variations ,and claims : which must contain cost to add to the budget and time to add to the time schedule .

 

The cost of the project with change in scope of project can go either up or down.But most likely it would go up,as you must have spent some time and money on the project even if its on initial stage.On the other side say if the project scope changes from high scale to smaller it will reduce the cost ,time taken would be more than what it would've taken if the scope of the project was kept same I.e. either large scale or smaller from start in this case.

Time will be increase, cost may be increase or remain as it was planned this depend on the new items of the new scope of project.

I agree with the expert by say that any changes in the project scope at any time and stage of the project will definitely affect the project costs and schedule, due to project triple constraint.

It depends on the type of contract and which party is changing the scope of works. If you have identified the scope of works and in the middle of the project you realize you made a mistake and identified the scope of works in a wrong way you need to start negotiating with your client. If the contract is lump sum then you can't ask for additional budget or changing the time frame. 

Obviously if the scope of the project is expanded the duration and the budget of the project will be expanded accordingly!

 

an study contributes to an improved understanding of duration extensions and their causes, by quantifying scope changes, differentiating amongst the various types of scope changes, and constructing an integrated model of work package duration extensions. and greater effect of external scope changes, compared with internal ones, on material orders, and thus on the total duration extensions.