Compare transit passes on value.
A travel pass is worth buying when the rides you will actually take exceed the break-even count, which is simply the pass price divided by the single fare. Comparing that threshold with your planned rides over the validity period is the whole decision, and it is a comparison people habitually get wrong in the pass's favour because they count the weeks they travel most rather than the average. The saving can be negative, which is the honest answer when the pass loses.
Break-even
Break-even rides = pass price / single fare
Comparison
Saving = rides per week x weeks x single fare - pass price
Only if you would genuinely have paid for them. Passes encourage trips you would otherwise skip, and counting those as savings is how a pass appears to pay for itself when it has not.
Where the network caps daily spend, pay-as-you-go already behaves partly like a pass and the break-even shifts. Use the capped amount rather than the raw single fare when your usual day hits the cap.