Premium alone doesn't tell you the real cost. Compare two plans by total spend, premium plus what you'd actually pay out of pocket, based on how much care you expect to use this year.
For each plan: you pay dollar-for-dollar up to the deductible, then a percentage (coinsurance) of costs after that, until you hit the out-of-pocket max, after which the plan covers 100%. Total cost is that out-of-pocket amount plus what you pay in premiums all year.
A lower monthly premium usually comes with a higher deductible and out-of-pocket max. That's a fine trade if you rarely use care. It gets expensive fast if you end up needing more than expected, which is exactly the scenario the crossover point above is showing you.
This only counts money your employer puts in on your behalf, since that's free money that directly offsets what a high-deductible plan costs you. It doesn't count your own HSA contributions, that's your own money moving from taxable pay into a tax-advantaged account, not a reduction in the plan's real cost. If you want to see the tax savings from your own contributions, that's a separate question, use the HSA vs FSA calculator for that side of the decision.
This models the standard deductible-then-coinsurance-then-max structure used by most PPO and HDHP plans. Plans with flat copays for office visits or prescriptions that don't count toward the deductible work differently, check your plan's summary of benefits if that applies to you. This also doesn't account for network differences or drug formularies, which can matter as much as the raw dollar comparison.