PAC simulator: the mix is the decision

A monthly plan is two decisions, not one: how much you put in, and what you put it into. This simulates both. Pick a ready-made mix or build your own, and see the expected value, the range the result realistically falls in, and how much of the return the fees take. Everything is computed in your browser, nothing is sent anywhere.

Start from a portfolio

Seven common ways to hold a portfolio. Click one to load it, then change anything you like, the moment you edit a weight it becomes your own mix.

Starting amount Monthly contribution Years

Your mix

Projected value: €0

Where each euro goes

All three exports carry the assumptions, not only the result: the mix with each class's weight, monthly amount, assumed return, volatility and TER, then the projection, the range and what the range means. A projected value without the assumptions behind it is a number, not a result, and in six months nobody remembers which figures produced it. The CSV is for a spreadsheet, with English column names and dots as decimal separators. The report is Markdown, in your language. The link carries the plan in the address itself, nothing is stored on any server.

How to read the range

The single number is the average outcome if the assumed returns hold exactly. It won't. The range around it is one standard deviation of the annualised return, which means roughly two outcomes in three land inside it, and one in three lands outside, including below. A wider range is not a flaw in the plan, it is the price of the return you are asking for. It narrows with time, which is the actual argument for a long horizon.

The assumptions, in the open

Each asset class carries a long-run nominal return, a volatility and a typical ETF running cost. They are rounded historical averages, not forecasts, and the past is a weak guide to the next twenty years. Portfolio volatility is not the weighted average of the parts: mixing assets that don't move together reduces it, so the model combines them assuming a 0.5 correlation between every pair. That is a stated middle ground, not a measured figure. Returns are nominal, so inflation is not subtracted, and taxes are not modelled at all.

What this can and can't tell you. It compares mixes under the same rules, which is the honest use. It does not predict your result. If you want the single-rate version with the fee drag broken out, use the compound interest calculator. To understand what you'd actually be buying, read how to read an ETF and automatic investing.

Educational tool, not financial advice, and not a recommendation of any portfolio or asset class. Returns are assumed constant and are never guaranteed, real markets swing and can fall for years. Interest is compounded monthly with contributions added at month end. Do your own research and consider a licensed advisor.

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