How Long Does a Systematic Review Take? A Realistic Timeline

The honest answer is: longer than most people planning one expect, and the gap between expectation and reality is usually the same few stages every time. A full systematic review, done properly, typically runs somewhere between four and twelve months from protocol to submission-ready manuscript — a wide range, but the width is the point. Scope, team size, and topic complexity move that number more than most planning accounts for.

Protocol development: 2 to 4 weeks

Before any searching begins, the question needs to be framed with PICO, eligibility criteria set, and the search strategy drafted and piloted. Reviewers new to this stage consistently underestimate it, because it feels like "just planning" — but a rushed protocol creates rework at every later stage, so time spent here is rarely wasted.

Systematic search: 1 to 3 weeks

Running the search across multiple databases, exporting results, and deduplicating records sounds mechanical, but a search across even three or four databases can return several thousand records before deduplication. Building and testing the search string well — the part people rush — determines how much unnecessary screening work happens next.

Screening: 4 to 10 weeks

This is usually the single longest stage, and the one most often underestimated in early planning. Title and abstract screening for a review with a broad topic can easily involve several thousand records; a well-run process uses two independent reviewers with a documented conflict-resolution method, which takes real calendar time even when both reviewers are working in parallel. Full-text screening of the shortlisted studies goes faster per record but still requires the same dual-review rigor.

Data extraction and risk of bias: 3 to 6 weeks

For each included study, extracting outcome data accurately and assessing risk of bias with the correct tool (RoB 2 for RCTs, ROBINS-I for non-randomized studies) takes meaningfully longer than it looks on paper, especially when double-extraction is used to catch errors — which it should be. This stage scales directly with how many studies made it through screening, which is one of the harder numbers to predict at the protocol stage.

Synthesis: 2 to 6 weeks

Meta-analysis, where the data supports it, requires model selection, heterogeneity assessment, and sensitivity analyses — not just running a pooled estimate and reporting it. Narrative synthesis, where meta-analysis isn't appropriate, takes real analytical time too, just of a different kind. Either way, this stage is where questions from earlier stages tend to resurface and need resolving.

Writing and PRISMA-compliant reporting: 3 to 6 weeks

Drafting the manuscript against the full PRISMA 2020 checklist, building the flow diagram so its numbers reconcile cleanly, and getting risk-of-bias and GRADE reporting into publication-ready shape takes longer than a first draft usually anticipates — particularly the flow diagram, which tends to need revisiting as inconsistencies in earlier counts surface.

What actually moves the total time

Team size matters more than almost any other factor — a solo reviewer doing everything sequentially, including dual-screening a second pass themselves, takes meaningfully longer than a team of two or three working key stages in parallel. Topic breadth matters just as much: a narrowly scoped clinical question with a handful of eligible studies moves far faster than a broad topic returning thousands of initial records.

If there's one planning mistake to avoid, it's treating screening as a short middle step. It's usually the longest stage in the entire process, and the stage most responsible for a systematic review's timeline slipping past its original estimate.