How do we do it?
What aspects do I need to focus on to build a rock-solid business case to hire more people?
One thing which would help is having some system to at the very least guesstimate your department workload. Saying "we are overworked" is not meaningful.
Saying something like:
- Our team receives 20 weekly requests
- Each request averages 10 hours work
- Our average time from request to completion is 3 months
- Each request adds $X to the company on average
- Our team has 3 members
- This allows us 120 hours/week
- We can only process 12 requests a week at maximum efficiency. This sort of crude estimation is only good if you have no meaningful metrics. In reality, your team is not going to be able to function at 100% efficiency and your time tracking/estimation needs to include this inefficiency. If you have more meaningful information or historical data from your projects (even anecdotal frustration from your team's customers) this can help get a better feel.
- We expect this workload to increase/stay the same/etc indefinitely
Why do it this way?
This information lets management determine:
- Are the projects important enough to justify additional headcount?
- Does there need to be a better prioritizing system?
- Perhaps your department needs to turn down requests.
- Implement a prioritization system where non-urgent requests are ignored unless all urgent ones are accomplished
- Is your average request time appropriate? Can workflow improvements help reduce the workload?
- Is another team overstaffed and those resources available for a reorg?
Data is everything in this. Saying "we're overworked" is meaningless. Presenting the above information is much much much more meaningful to management.
Historical information is even better to have.
When is best?
Keep in mind too that if you add headcount at a critical point in a project, you might actually make the project take longer. If your team is overwhelmed indefinitely this doesn't really matter (you will have to take the hit sometime). However if you are hoping to launch a project in a few months, adding lots of interview, HR, and onboarding time to an already overworked team is not necessarily the best idea.
However only delay this work if there is a reprise in sight.
What if no one cares?
You might run into situations where no one cares. Or basically says "whatever, the department works, no problems yet." Or your manager not wanting to take action for a variety of reasons.
Then you need to determine if a stressful job is worth it to you. If managers feel no "pain" they will not add headcount. You need to basically determine if this environment is one you are willing to work in - if not, act accordingly.
Keep in mind too the process for adding headcount can be a long process even when your boss, your bosses boss, and perhaps even more levels higher agree.
Overall company performance, budgeting, forecasting, etc all factor into whether this is possible.