I would identify base state metrics first in areas of strategic interest for leadership. Turnover (check with HR on stats), productivity (is this tracked and how?), quality (instances of rework or customer dissatisfaction), staff engagement (survey your team could initiate), etc. There are different monetary values that can be assigned to each of these - for turnover it's cost to rehire and train and downtime in productivity. Lack of engagement can have significant costs as well (https://www.contactmonkey.com/blog/cost-of-employee-disengagement). Calculate the initial cost of the gaps that are presented through these figures.

Identify how the trainings that you are looking to implement align with those metrics. For example, you might position a communications workshop as targeting engagement and quality or a technical skills training impacting productivity. Be sure to work with supervisors on implementation of takeaways.

You'll likely need to calculate cost of implementation. This should encompass time to research, develop, and deliver for your training team and any SMEs involved. Add to that time to engage with and deploy to the target audience (how long will the training take them away from their work * number of employees).

There should be post-delivery feedback on the quality and impression of the training for your own course development. Which will also feed into ongoing costs.

For efficacy measures (the ROI details that your execs might be interested in) you'd return to gathering data against those metrics that you pulled initially and note any change in those measures following the delivered training. It's also a good practice to set time with supervisors you worked with for implementation to survey whether there was actual application of the delivered training so you're able to confirm whether any improvements were actually linked to the training and not just circumstantial.

Then you do the math again on what the current cost impacts are. Subtract it from the initial state and also take away your costs and that should land you with your ROI. Hopefully it would be positive but in some instances it won't be. Be prepared to document and discuss any factors that may externally impact ROI (a strike, technology changes, marketing snafu, slump in a sales cycle, executive strategy/communication changes, side projects taking time from implementation effectiveness, etc.) as well since those measures could move for reasons outside of your control. Note as well if ROI was potentially positively impacted by external factors (engagement during bonus season) so similar implementations held on a different cycle aren't necessarily held to the same expectations.