Loading page
Feature checklists make every tool look equivalent. This table leads with the three things that actually differ — what it costs you before it works, whether your files leave your device, and where the free version stops.
| Omni Calculatoromnicalculator.com | Sleep Foundationsleepfoundation.org | Drugs.com Interaction Checkerdrugs.com | ExRx.netexrx.net | |
|---|---|---|---|---|
| What it does | Around 3,000 small calculators, each with the formula shown underneath | Explains sleep with a medical review panel, plus bedtime and cycle calculators | Lists the interactions between the medicines, supplements and alcohol you enter | An exercise library that names the muscles each movement actually works |
| What it costs you | No sign-upWorks the moment the page loads. No account, no email, no trial. | No sign-upWorks the moment the page loads. No account, no email, no trial. | No sign-upWorks the moment the page loads. No account, no email, no trial. | No sign-upWorks the moment the page loads. No account, no email, no trial. |
| Your files | Runs on their server | Runs on their server | Runs on their server | Runs on their server |
| Where it stops | Health calculators here are population-level estimates with wide error bars — useful for orientation, not for a decision about treatment. | It is general education, not medical advice — persistent sleep problems need a clinician, and the site funds itself partly through mattress reviews. | It cannot see your dose, your kidney function or your other conditions, so it flags possibilities for a pharmacist or doctor to judge — never stop or change a medicine on its say-so. | The interface is dated and search is weak, and some calculators and articles sit behind a paid Premium tier. |
| Best for |
|
|
|
|
| Category | Health & Everyday Life | Health & Everyday Life | Health & Everyday Life | Health & Everyday Life |
| Last checked | 2026-07-29 | 2026-07-29 | 2026-07-29 | 2026-07-29 |
| Open the site | Open | Open | Open | Open |
This comparison is in the address bar — copy the URL to send it to someone.