Do I need a calendar app AND a journal app, or can one do both?

Short answer: you don't need two apps, but plenty of people run two anyway, usually out of habit rather than necessity.

The split happens because calendar apps and journal apps solve different problems. A calendar answers "what's happening and when." A journal answers "how did that go, and how do I feel about it." Since most calendar apps (Google Calendar, Outlook, Apple Calendar) have no reflection feature at all, and most journal apps (Day One, Journey) have no real scheduling, people end up with one of each by default, not by choice.

The problem isn't having two tools. It's that the journal usually loses. Your calendar gets checked automatically, every day, because things depend on it: you'll miss a meeting if you don't look. Your journal has no equivalent pressure. Nothing breaks if you skip it, so it's the first habit to slip in a busy week, and the app you open least is the app you eventually stop opening at all.

When it actually makes sense to combine them

If your journaling is meant to be a daily habit tied to your day (an evening reflection on what happened, your mood, something you're grateful for), putting it right next to the calendar you already check removes the one extra step, opening a second app, that habit-tracking research keeps coming back to as the biggest single point of failure. This is the specific problem PlanJour is built around: a real calendar (recurring events, categories, reminders) with a daily journal page one tap away, so the evening reflection prompt shows up right after you've looked at what the day held.

When it's fine to keep them separate

If your journal is a longer-form writing practice, morning pages, processing a specific situation, creative writing, and it doesn't need to be daily or tied to your schedule, a dedicated writing app with more text-formatting depth might genuinely serve you better. The combined approach is specifically a fix for the "I keep forgetting" problem, not a universal upgrade over every standalone journal app.

A simple way to decide

Ask yourself which describes you: "I want to journal every day but keep forgetting," or "I journal when I have something to process, and that's fine." The first is a habit-formation problem, and combining the tools tends to help. The second is a different use case entirely, and a separate app isn't costing you anything.

If it's the first one, worth trying a combined app for a couple of weeks before assuming the problem is you rather than the setup. Habits that depend on remembering to open an extra app have a structural disadvantage no amount of willpower fully offsets.