"When will I have £X?" isn't one date — it's a spread of maybes. This runs 600 possible futures and tells you the honest version: how likely you are to get there, how soon if you're lucky, and how long if you're not.
Where you start, what you add, what you assume.
How it works: 600 randomly-drawn futures, each growing at your return with your bumpiness and monthly top-ups. We note the first time each one touches your goal. "Typically" is the middle of those times; the lucky/unlucky figures are the fastest and slowest tenth. A hypothetical model on steady assumptions — real markets are messier. Not advice.