Why catalyst windows like "H2 2026" are vague, and how they narrow

Only a small share of the catalysts on this site have an exact date. When this guide was written, fewer than one in seven upcoming rows did, and nearly all of those were PDUFA dates. Everything else is a window: "Q4 2026", "H1 2027", "mid-2027". That isn't the tracker being lazy. A window is usually the most precise thing anyone outside the company knows, and how a window changes over time is information in itself.

Why companies give windows, not dates

A PDUFA date is set by the FDA under a published formula (how that works). A clinical readout has no equivalent. Its timing depends on things the company only partly controls:

Enrolment. How fast sites find and sign up eligible patients. Rare diseases and crowded indications are slow.
Follow-up. Every patient has to reach the final visit the protocol specifies, say week 52, before the primary analysis can be done.
Events. Many oncology and cardiovascular trials are "event-driven": they read out when a pre-set number of events (disease progression, heart attacks, deaths) has occurred, which nobody can schedule.
Data cleaning and database lock. After the last visit, the data are checked and queried, the database is locked, and only then is it unblinded and analysed. That alone takes weeks.
Regulatory interactions. Submission timing often hangs on a meeting with the FDA whose date the agency sets.

There's also a legal reason. Timing guidance is a forward-looking statement, and companies give it alongside cautionary language about the risks that could change it, which is what the US safe-harbour rules for forward-looking statements expect. A window that turns out to be right is better for a company than a date that turns out to be wrong.

What the phrases usually mean

Q1, Q2, Q3, Q4: calendar quarters, January–March and so on, unless the company says otherwise.
H1 / 1H and H2 / 2H: the first half (January–June) and second half (July–December).
Early, mid, late: loose. "Mid-2027" usually means around the middle of the year, give or take a couple of months; companies don't define it.
"By year-end" or "in 2027": the whole period is in play. Treat it as the end of the window, not the start.
"Near-term", "in the coming months": no window at all.
Fiscal years: a few companies run non-calendar fiscal years, so "fiscal Q3" can be a different calendar quarter. The filing will say.

From the tracker

CG Oncology's filing described a Phase 3 topline result as "anticipated in the near-term" (8-K exhibit). Since that isn't a window, the row is marked Needs check and its note says the year shown is a placeholder, not guidance. See the CG Oncology page.

How windows narrow

A window usually tightens as the trial moves through operational milestones, and companies tend to announce each one:

Enrolment complete (or "last patient dosed"). From here the readout timing is mostly arithmetic: the follow-up period plus a few months.
Last patient, last visit. All the data that will be collected has been collected.
Database lock. The data are final. Topline results often follow within weeks.

The guidance itself also moves: "2027" becomes "H1 2027", then "Q2 2027". The best place to see this is the company's quarterly results release, which restates its milestones every three months (why that release matters). Presentations at investor conferences are the other common place timelines get updated.

How windows slip

Windows also move later, and companies rarely put it plainly. Signals to look for:

The window moves. "Q4 2026" becomes "early 2027", or "H1" becomes "mid-year".
The window widens. "Q3" becomes "second half".
The language softens. "On track for" disappears, or "data expected" becomes "data anticipated".
The milestone changes shape. A planned topline readout becomes an "interim update", or a submission becomes a "regulatory interaction".

From the tracker

Ocugen's Phase 2/3 Stargardt trial had an interim analysis due in Q3 2026. When the interim came, the independent monitoring committee recommended continuing with longer follow-up, and the company now guides to topline data in mid-2027 (8-K exhibit, 8 September 2026). The Q3 event happened on schedule, but it was a check-in rather than the efficacy result, and the topline result now sits in a window most of a year later. See the Ocugen page.

When a window closes with no news

If a quarter ends and the company hasn't reported the readout it guided to, that's information too. Companies sometimes report at the very end of a window, or at the next results release a few weeks later, and sometimes the slip is only acknowledged then. Nobody outside the company can tell which until it says so, so the right move is to check its latest filings rather than assume.

On this site, a row stays "upcoming" until the company reports an outcome or new guidance, and then it's updated with the filing that says so. If you spot a row whose window has closed and the company has said something we've missed, tell us.

How the tracker handles windows

Precision is kept, not invented. A window shows as written ("H1 2027"), never as a guessed day.
No countdown. Only exact dates get a "in 23d" countdown. Windows are labelled "company guidance".
Windows sort behind real dates. When you sort by date, a window sits after every exact date in the last month it covers: Q1 at the end of March, H1 and Q2 at the end of June, Q3 at the end of September, and H2, Q4 or a whole year at the end of December. Dated events always come first, and where a window sits in the list is not a prediction of when inside it the event will land.
Calendar feed is exact dates only. The calendar feed leaves windows out, because an all-day event for "H1 2027" would just be noise in your diary.

The methodology page has more on how dates and windows are recorded.

More guides

What a PDUFA date is, and why the FDA doesn't publish themThe PDUFA target action date is the FDA's own deadline for deciding on a drug application. Here is where it comes from, how it moves, and why you only hear about it from the company.
What happens at an FDA advisory committee meetingWho sits on an FDA advisory committee, how the day runs, what the vote means and doesn't mean, and where to find the documents beforehand.
What a Complete Response Letter means, and what usually followsA Complete Response Letter is the FDA's "not yet" on a drug application. What it contains, the company's options, how resubmission clocks work, and how to read the announcement.
How to read a Phase 3 topline readoutEndpoints, p-values, effect sizes, safety tables and the phrase "met its primary endpoint": a practical guide to reading the press release a company puts out when pivotal trial results land.
Clinical trial phases explained: Phase 1 to Phase 4What each phase of clinical development is for, roughly how big the trials are, what the in-between labels like 1b, 2a and 2/3 mean, and what a readout at each stage can and can't tell you.
NDA vs BLA: the two kinds of US drug applicationWhy some products are filed as a New Drug Application and others as a Biologics License Application, who reviews each, what supplements and rolling submissions are, and why the difference matters after approval.
Fast Track, Breakthrough, Priority Review and Accelerated Approval explainedThe FDA's expedited programmes are often lumped together, but they do different things at different stages. What each one is, what it changes about the timeline, and what it doesn't promise.
How to verify a catalyst date yourself on SEC EDGARA step-by-step walkthrough of the method behind this site: finding the filing that announced a PDUFA date or readout window, reading it properly, and spotting the traps that catalyst calendars fall into.
8-K vs 6-K vs press release: where catalyst dates are disclosedWhy almost every row on this site links to an 8-K exhibit, what the 6-K is for, when a press release has no filing behind it, and how the item numbers and "furnished vs filed" affect what you're reading.
Glossary of FDA and biotech catalyst termsPlain-English definitions of the regulatory, clinical and SEC-filing terms used across the tracker and the guides, from AdComm to Type A meeting.