Math nerds: When is GoodRx worth it if I have insurance?

I have a high-deductible insurance plan that covers 80% after the deductible is met. I'm not sure if I'm going to meet my deductible this year, but there is a fair chance I will since it is shared with my family.

I can get prescriptions through a covered mail-in pharmacy but I can get them cheaper using a GoodRx coupon. For some prescriptions I exclusively use GoodRx because the difference is like $100 vs $10, but for others it is more like $50 vs $40 and I'm wondering if the benefit of paying down my deductible outweighs the benefit of saving $ without going against my deductible.

If I assume I'm going to eventually meet my deductible, it seems intuitive to me that I should only go with the GoodRx coupon if it gives at least an 80% discount, since paying full price now and saving 80% on a later expense due to meeting my deductible sooner is equivalent to saving 80% now and paying a later expense at full price. Is that intuition correct? Can anyone share a formula for calculating the break-even discount rate if my other expenses *don't* meet my deductible, so I would only get the discount if I consistently use the covered pharmacy?

submitted by /u/Cakoluchiam
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