Sign up for a local 5K and the internet will immediately offer a twelve-week plan, a heart-rate zone chart, and a shopping list. None of it is required to cover three miles on a Saturday morning.
Most community 5Ks are full of people walking, pushing strollers, and stopping for water. The finish line doesn't check your spreadsheet.
Walk breaks are allowed
Run a minute, walk a minute. Walk the hills. Walk the whole thing if that's what the day calls for. The distance is the same either way.
Starting with an interval you can actually repeat is how people get to a second race. Going out too fast in the first half mile is how they spend the rest of the event regretting it.
You don't need new gear
Whatever sneakers you already walk in are fine for a first one. A water bottle, weather-appropriate clothes, and a safety pin for the bib cover it.
The one thing worth doing: try a couple of short loops before race day so nothing is brand new — not the shoes, not the distance, not the breakfast.
Don't rebuild your calories around it
A 5K is a modest chunk of a week, and the activity multiplier in the calculator already describes a week that includes some movement. You don't need a special race-day diet or a big refuel that turns into a second lunch.
Formulas carry roughly 10–20% individual error, and one Saturday morning sits well inside that. If running becomes a three-times-a-week habit for a month, then the activity setting is worth another look.
The actual goal
Finish, feel okay the next day, and be willing to do it again. That's a better outcome than a fast time followed by two weeks of sore shins.
If you have a heart condition, an injury, or any medical concern, check with a professional before starting. Otherwise, pin the bib on and go.