How to Conduct Software Estimations: Traditional vs Scientific Estimates


One of the first ques­tions asked when un­der­tak­ing any type of pro­ject is usu­ally how much will it cost? It’s a rea­son­able ques­tion to ask, be­fore mak­ing a de­ci­sion it’s only nat­ural to want all the facts at hand. There are some in­dus­tries where this has be­come the norm - the paint­ing and con­struc­tion in­dus­tries come to mind. However, this is vastly dif­fer­ent in the soft­ware in­dus­try.

This ar­ti­cle is de­signed to un­pack the soft­ware es­ti­ma­tion process and the dif­fer­ent ap­proaches used in the in­dus­try.

The in­dus­try

Generally the next fol­low up ques­tion asked is why can’t you tell me ex­actly how long it will take? Software dif­fers to other in­dus­tries as it deals pre­dom­i­nantly with un­knowns. Every piece of soft­ware is de­signed to be dif­fer­ent in one way shape or form, oth­er­wise there is no unique value propo­si­tion. Couple that with the fact that tech­nol­ogy con­tin­ues to im­prove rapidly, with a new ‘industry stan­dard’ emerg­ing every cou­ple of years and it be­comes in­cred­i­bly un­likely that a soft­ware de­vel­oper will build the same ap­pli­ca­tion, the same way, twice.

The prob­lem with soft­ware es­ti­mates

There is a so­ci­etal prob­lem when it comes to es­ti­mat­ing work. In many in­stances the cheap­est es­ti­mate wins the work. This would­n’t be an is­sue pro­vided the es­ti­mate was ac­cu­rate and did not im­pact the qual­ity of the pro­ject. So if the pro­ject blows out or the qual­ity is not up to scratch, does the blame rest with the de­vel­op­ment com­pany for low-balling the pro­ject or the cus­tomer that chose the cheap­est op­tion? With a greater knowl­edge and un­der­stand­ing of the es­ti­ma­tions process, we can move away from this cy­cle.

When to es­ti­mate

There are many com­pet­ing lines of thought here with dif­fer­ent strate­gies rec­om­mended based on which phase the pro­ject is in. For the pur­pose of this ar­ti­cle we’ll break a pro­ject into the com­mon stages; ideat­ing, scop­ing and de­vel­op­ing.


Before the pro­ject is prop­erly scoped it is still in an ideation phase. This means all the re­quire­ments are not yet known.


This is one of the more pop­u­lar ap­proaches to un­der­take when the soft­ware is at such an early stage. Based on the soft­ware de­vel­op­ers prior ex­pe­ri­ences and gut feel­ing they may give a broad bracket as to the length of time based on a few cen­tral re­quire­ments.

Historical com­par­i­son

If the com­plex­ity and size of the pro­ject sounds sim­i­lar to a past pro­ject than the es­ti­mate given may sim­ply be the time it took to build the past pro­ject.

The prob­lem with giv­ing an es­ti­mate this early on in the process is that there are so many un­knowns. Generally, the client will bud­get and set their ex­pec­ta­tions based on a very early stage es­ti­mate (if it has been given). What hap­pens when the scope is un­packed and the ini­tial es­ti­mate is in­ac­cu­rate? It cre­ates ten­sion and im­pacts the trust be­tween the soft­ware de­vel­op­ment com­pany and the cus­tomer.

No de­vel­op­ment es­ti­mate

WorkingMouse’s pre­ferred ap­proach to es­ti­mat­ing a pro­ject be­fore it is scoped is sim­ple. We don’t. We can es­ti­mate the time it will take to prop­erly scope the pro­ject based on its com­plex­ity but we do not have enough in­for­ma­tion to es­ti­mate de­vel­op­ment time.


T-Shirt sizes

This ex­er­cise is one of rel­a­tiv­ity. By mark­ing func­tion­al­ity as XS, S, M, L, XL (and so on) we can group to­gether sim­i­lar pieces of func­tion­al­ity. It’s gen­er­ally much faster than tra­di­tional time based es­ti­mates.

Once the tick­ets are grouped, es­ti­ma­tion val­ues can be put to each group. For ex­am­ple, an XS ticket may on av­er­age take 2 hours to com­plete. In a short space of time, the de­vel­op­ment team and prod­uct owner can start gaug­ing the rel­a­tive size of the ap­pli­ca­tion. Keep in mind, the es­ti­mate can still be in­ac­cu­rate at this stage.

Fibonacci es­ti­ma­tions

As men­tioned above, soft­ware es­ti­ma­tions are in­her­ently quite dif­fi­cult. The Fibonacci-type ap­proach to es­ti­ma­tions tries to sim­plify things. It is based on the the­ory that the big­ger some­thing is, the less pre­cise we can be. It is rea­son­able to as­sume that a small piece of func­tion­al­ity can be es­ti­mated down to the hour. However when we start look­ing at big­ger pieces of func­tion­al­ity, for ex­am­ple com­plex API in­te­gra­tions, which have a high de­gree of com­plex­ity and dif­fi­culty, we can­not be that pre­cise. It may take be es­ti­mated to take a week or 3 days but it would be bold and ul­ti­mately un­wise to es­ti­mate that it will take 1 week, 1 day and 2 hours.

It is rec­om­mended to wait un­til the end of scope, once all the im­me­di­ate func­tion­al­ity is known to hold an es­ti­ma­tions ses­sion. Without stake­hold­ers aligned on the ac­cep­tance cri­te­ria of each piece of func­tion­al­ity and its im­pact across the wider ap­pli­ca­tion, it is dif­fi­cult to en­sure the ac­cu­racy of the es­ti­mates.

Planning poker

This is a slightly dif­fer­ent way of run­ning the Fibonacci ap­proach to es­ti­mat­ing. Everyone is given a set of cards with lengths of time. It’s de­signed to en­sure that one team mem­bers es­ti­mate (the first to speak) does­n’t in­flu­ence other team mem­bers es­ti­mates.


During a plan­ning ses­sion

During de­vel­op­ment, plan­ning ses­sions oc­cur at the be­gin­ning of each it­er­a­tion (or sprint). It gives the de­vel­op­ment team an op­por­tu­nity to learn from ear­lier it­er­a­tions. It also gives them an op­por­tu­nity to feed learn­ings back into the es­ti­ma­tions.

Let’s say for ex­am­ple af­ter two it­er­a­tions a de­vel­oper was able to lever­age a React li­brary more than ini­tially an­tic­i­pated. That might bring the es­ti­mates for some func­tion­al­ity down, al­low­ing more to be com­pleted dur­ing the it­er­a­tion. On the other hand, there may be a com­pli­ca­tion that means cer­tain func­tion­al­ity takes longer than ini­tially ex­pected. By elab­o­rat­ing on es­ti­ma­tions dur­ing the plan­ning ses­sion, the de­vel­op­ment team has the most re­cent in­for­ma­tion avail­able to make an es­ti­mate.

Types of es­ti­ma­tions

While all the tech­niques listed above are help­ful, it’s more im­por­tant to dis­tin­guish be­tween tra­di­tional es­ti­ma­tions and how they’ve been re­fined to em­brace a more sci­en­tific ap­proach.

Traditional soft­ware es­ti­ma­tions

These are quite sim­ply es­ti­mates against func­tion­al­ity. By ask­ing how long will “X” take and do­ing some sim­ple ad­di­tion, gives you the tra­di­tional pro­ject es­ti­mate.

The is­sue with this ap­proach is that it fails to cap­ture a num­ber of other fac­tors that have a ma­jor im­pact on time. For ex­am­ple, it is un­re­al­is­tic to be­lieve that 100% of a de­vel­op­ers day will be spent work­ing on a pro­ject. There are plan­ning meet­ings, morn­ing hud­dles and com­pany-wide meet­ings that im­pact pro­duc­tiv­ity.

Scientific soft­ware es­ti­ma­tions

By un­der­stand­ing and mea­sur­ing the im­pact that other fac­tors have on de­vel­op­ment time, we can be more sci­en­tific in our es­ti­ma­tions. After run­ning an ex­per­i­ment over a num­ber of pro­jects we found the fol­low­ing fac­tors also im­pacted de­vel­op­ment length;

  • Allocation to meet­ings out­side the pro­ject
  • Risk
  • Cleaning up the code­base and time to fo­cus on qual­ity
  • Time to in­ves­ti­gate highly com­plex fea­tures.

Each of these fac­tors have a mul­ti­plier based on the im­pact that they have on es­ti­mates. As men­tioned above, a rushed pro­ject can detri­men­tal to the qual­ity of the ap­pli­ca­tion. It is ab­solutely nec­es­sary to take these fac­tors into con­sid­er­a­tion in or­der to ac­cu­rately set ex­pec­ta­tions.

Risk is the most com­plex fac­tor to mea­sure. As a gen­eral rule, some pro­jects are riskier than oth­ers. So then, how do we cap­ture risk? Our ap­proach is to sep­a­rate risk into two con­tribut­ing fac­tors; com­plex­ity and un­fa­mil­iar­ity. These are mea­sured on a 1-5 scale for each piece of func­tion­al­ity. The higher the risk, the greater the es­ti­mate for that func­tion­al­ity.

To sum­marise

If you’ve got­ten this far, well done. While the sci­ence be­hind soft­ware es­ti­ma­tions may not ex­cite many, there is no ques­tion that they have a huge im­pact on the suc­cess of a pro­ject. Start with an in­ac­cu­rate es­ti­mate and you’ll find your­self on the back-foot, of­ten at the ex­pense of qual­ity.

My ad­vice is to ask your de­vel­op­ment com­pany how they ap­proach the es­ti­ma­tions process. If they’re will­ing to give a quote or es­ti­mate be­fore the scope is fully fleshed out and agreed upon, that should be a red flag. Also ask about the al­lowances they have for nec­es­sary work that is­n’t fea­ture de­vel­op­ment. If you’d like to see how es­ti­ma­tions are in­cluded in our process, please down­load the Way of Working.

Discover Software


Yianni Stergou

Marketing en­thu­si­ast and FIFA ex­tra­or­di­naire

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