Clinical Trial Visit Window Calculator
Generate target, earliest and latest clinical study visit dates using protocol-defined offsets, asymmetric windows and optional working-day rules.
Do not enter participant-identifying information
No names, initials, participant/subject IDs, MRNs or dates of birth — anywhere on this page, including in visit labels. Nothing you enter is saved or sent anywhere; it stays in your browser only, for this visit.
Choose the exact event used as the scheduling origin in the current approved protocol or Schedule of Activities. Consent, screening, baseline, randomization and first dose are not interchangeable.
This calculator uses one fixed starting event for the schedule. If the protocol calculates a visit from another event — such as last dose, end of treatment or an actual prior visit — create a separate calculation. Per-visit dependencies are not supported.
Loading today's date…
| Visit | Day | Target date | Earliest | Latest | Assumptions |
|---|---|---|---|---|---|
| Baseline | Loading today’s date… | ||||
| Visit 2 | Loading today’s date… | ||||
For educational purposes only. This tool does not replace, interpret, amend or override the current approved study protocol, protocol amendments, sponsor instructions or applicable site procedures under any circumstances. Always verify every result against the applicable study documents before use.
Adjustment rules and assumptions above are also summarized in each row’s Assumptions column. Working-day tolerance excludes Saturdays, Sundays and the custom holidays you add above only — there is no automatic country or regional holiday database.
“Download target dates” and “Download visit windows” each produce a .ics file you can import into Google Calendar, Outlook or Apple Calendar. Imported events are a snapshot: they do not update automatically if you change the calculation above, and nothing you enter is saved or transmitted by DaysHoursCalculator. These files are stored wherever your calendar app keeps them — double-check that visit labels above contain no participant-identifying information before exporting. Protocol and approved study documents take precedence over any calendar entry.
Standards context
- ICH E6(R3): explains that clinical trial protocols should be clear, scientifically sound and operationally feasible, and that trial conduct is governed by the approved protocol and its amendments.
- ICH M11/FDA: recommends that allowable windows be stated for all visits and procedures in a trial’s schedule of activities.
These references provide standards context only. They do not validate this calculator, prescribe its date arithmetic, or establish regulatory compliance. The current approved protocol, amendments, sponsor instructions and applicable site procedures always take precedence.
How this calculator works
Name the schedule's starting event (for example, informed consent, randomization or first dose / C1D1) and set its date, then add as many visit rows as your protocol's schedule of events needs. Each visit is computed independently from that one starting event — never chained from another visit's own result, and never from a different event such as last dose or an actual prior visit; a schedule that depends on more than one starting event needs a separate calculation.
Choose whether the starting event counts as Day 0 or Day 1 (with no Day 0) — both are real conventions used across different protocols and institutions, and this page treats it as a calculation choice you make to match your own protocol, not a universal rule it enforces on you. For a day-based visit, enter the protocol's own scheduled study-day number directly — entering "14" always means Day 14, computed correctly whether that's 14 days after the starting event (Day 0 convention) or 13 days after it (Day 1 convention, since the starting event itself is already Day 1). Switching the convention recalculates every day-based visit's actual date to match your new choice, not just its displayed label. Week, month and year offsets are a separate, explicit elapsed count from the starting event and are never affected by this convention.
Each visit's early and late tolerance can differ — a target of Day 28 with a −3/+7 window is a normal asymmetric case, not a special one. Set both to 0 for a locked, zero-width target date.
Tolerance can be counted in calendar days or working days. Working-day tolerance skips weekends and the custom bank/site holiday dates you add below; there is no automatic country or regional holiday database, since holiday calendars depend on jurisdiction, region and year. An optional adjustment can move a visit's target date to the nearest previous or next working day — the page always shows the raw calculated date alongside the adjusted one when they differ, and flags a row if that adjustment would push the target outside its own earliest–latest window.
Calendar-month and calendar-year offsets preserve the day of month when possible, clamping to the target month's final valid day when it doesn't have that day (for example, one month after 31 January lands on 28 or 29 February).
Below the results table, a calendar view shows each visit's target date and its earliest–latest window one month at a time — useful for spotting overlapping windows at a glance. The detailed table remains the complete, authoritative record.
Copy the results table for pasting into a spreadsheet, download it as a CSV file, or download a calendar (.ics) file — target dates only, or full visit windows — for import into Google Calendar, Outlook or Apple Calendar. All of these are generated entirely in your browser. Nothing you enter is saved, sent anywhere, or available on a future visit.
The tool is arithmetic only. Where legal, payroll, holiday, timezone or jurisdiction-specific rules matter, the page states what is and is not included.
Frequently asked questions
Is this validated for clinical trial or regulatory compliance?
No. This is a general-purpose planning arithmetic aid, not a validated clinical system, a source document, a protocol deviation checker, or a claim of HIPAA or other regulatory compliance or conformance. For educational purposes only — it performs the date math you configure and nothing more. The current approved protocol, its amendments, sponsor instructions and applicable site procedures always take precedence, and every result should be verified against them.
Should I use Day 0 or Day 1?
Whichever your own protocol defines. Both conventions are genuinely used across different studies and institutions — this page doesn't assume one is correct. For a day-based visit, enter the study day exactly as your protocol states it (for example, "Day 14"); the calculated date and the displayed day label always match what you entered, under either convention. Switching conventions recalculates the date — it doesn't just relabel it, so double-check your visits after changing this setting. Day 0 is rejected outright under the Day 1 convention, since there is no Day 0 to enter in that case.
Does this know my country's public holidays?
No. There is no automatic country or regional holiday database. Add the specific bank or site holiday dates that matter for your calculation, and they'll be excluded from working-day tolerance and the working-day adjustment.
Is any participant information stored or transmitted?
No. This page has no fields for participant name, initials, ID, MRN, date of birth, or any uploaded document — don't enter identifying information anywhere, including in visit labels. Whatever you type exists only in your browser for this visit; closing or reloading the page clears it.
What's the difference between this and the Workday Calculator?
The Workday Calculator computes one resulting date from one offset. This page generates a full multi-visit schedule from a single starting event — each visit with its own offset, asymmetric early/late tolerance, and optional working-day rules — the workflow a protocol's schedule of events actually needs.
Can I export the schedule?
Yes. "Copy table" copies a tab-separated version of the results to your clipboard for pasting into a spreadsheet, "Download CSV" saves a CSV file, and two calendar-file buttons download a .ics file — one all-day event per visit on its target date, or one multi-day event per visit spanning its earliest–latest window — for import into Google Calendar, Outlook or Apple Calendar. Everything is generated entirely in your browser and disabled until every visit row has valid values. Imported calendar events are a snapshot: they don't update automatically if you change the calculation, and the files have no fields for participant-identifying information — double-check your visit labels before exporting.