Upvote:3
The minimum period for a Swiss Rail Pass is 3 days. I do believe you will make that back on you itinerary, if you include the lake cruises and the Jungfraujoch, which appears to be only a 25% reduction, not free. That link has the full map of covered lines.
The pass also admits you to most museums, on the off-chance you are inside for more than a few minutes of this itinerary.
Upvote:3
If you are less than 26 years of age, you can buy 3 day youth travel pass for 198CHF (rather than 232CHF for adult pass). The pass allows you free lake rides, free local transport, free travel on normal trains and postbuses and free or reduced entry to most museums. The savings on mountain rail and cable cars range from 25-50%. You can check the map
The pass will cover your travel from the moment you arrive in Geneva till you depart Zurich (You may have to buy it in advance because Geneva/Airport counters may not be manned if you arrive at night). Depending on your plan you can check point to point ticket cost (even for boats) on SBB website and compare costs. But IMO travel pass will be cheaper (especially if you are eligible for youth pass).
An added advantage of pass is that you can be flexible in your plan. You reach Interlaken and find you don't have much time for the mountain. Just take the train to lauterbrunnen and cable care to murren to enjoy scenery for free!
Also you can include places that offer more savings to make your money back. Maybe go to Zermatt (50% off on Gornergrat rail and matterhorn glacier paradise and both together are cheaper than jungrafu) rather than Jungfraujoch. You can drop Thun lake ride to squeeze in a visit to Luzern (through beautiful golden pass brienz-luzern line after the must do interlaken brienz boat ride) while on your way to Zurich.