Compares how groups of users who started together return over time.
<div class="stage"><div class="label">WEEKLY RETENTION · ILLUSTRATIVE</div><svg viewBox="0 0 300 135" preserveAspectRatio="none"><path class="axis" d="M25 5 V115 H295"/><path class="old" d="M25 15 L78 48 L132 73 L185 91 L239 101 L290 107"/><path class="new" d="M25 15 L78 36 L132 50 L185 59 L239 65 L290 70"/><text x="225" y="58">NEW</text><text x="225" y="90">OLD</text></svg><div class="weeks">W0 W1 W2 W3 W4 W5</div></div>.stage{position:relative;width:min(94vw,760px);height:min(88vh,310px);font:800 clamp(10px,max(3.4vmin,1vw),15px)/1.25 sans-serif}.stage *{box-sizing:border-box}.label{font-size:clamp(10px,max(3.4vmin,1vw),12px);letter-spacing:.1em;color:var(--muted)}.accent{color:var(--accent)}.pill{border:1.5px solid var(--fg);border-radius:999px;background:var(--surface);padding:.5em .8em}.hint{position:absolute;right:2%;bottom:0;font-size:clamp(10px,max(3.4vmin,1vw),12px);color:var(--muted)}.stage svg{position:absolute;left:4%;top:20%;width:92%;height:64%;overflow:visible}.axis{fill:none;stroke:var(--line);stroke-width:2}.old,.new{fill:none;stroke-width:5;stroke-linecap:round;stroke-dasharray:450;animation:trace 4s ease-in-out infinite alternate}.old{stroke:var(--fg)}.new{stroke:var(--accent);animation-delay:.3s}svg text{font:900 12px sans-serif;fill:var(--fg)}.weeks{position:absolute;bottom:3%;left:7%;font-size:clamp(10px,max(3.4vmin,1vw),12px);white-space:pre;color:var(--muted)}@keyframes trace{from{stroke-dashoffset:450}to{stroke-dashoffset:0}}Cohort retention groups people by a common start, such as signup week, and tracks continued core actions. An overall active-user count can hide churn behind new acquisition.
The demo overlays an older and an improved cohort. Align cohort size, observation window, and the definition of return before comparing them.
Use it to assess whether onboarding or product changes affect repeat use.