Důchod, renta a FIRE
How Much to Save Monthly to Reach Rent X?
Key takeaways
- The result depends critically on your assumptions — return, inflation, time horizon.
- The earlier you start, the less you need to save monthly thanks to compound interest.
- A conservative return of 5–6% per year is a more realistic baseline than an optimistic 10%.
- The calculation is a starting point — update your projection once a year.
- A small change in assumptions (by 1%) can shift the result by tens of percent.
The calculation of your monthly contribution toward a retirement income starts from a simple equation: you need to know the target portfolio size, the assumed annual return, and the number of years until you stop working. But the resulting number is only as accurate as your assumptions — and nobody knows those in advance.
The Basic Logic
First, you determine your target portfolio (see calculating your path to retirement income). Then you find the monthly contribution that, at the given return over the given number of years, will grow to that amount. The power of compound interest works in your favor here — every year earns not just on your contributions, but on all previous gains as well.
- 30-year horizon, 6% return: a monthly contribution of CZK 5,000 grows to ~CZK 5 million
- 20-year horizon, 6% return: the same contribution grows to only ~CZK 2.3 million
- 30-year horizon, 8% return: the same contribution grows to ~CZK 7.5 million
The difference between a 20-year and 30-year horizon is dramatic. Every additional year matters enormously.
The Impact of Assumptions
The return is the variable that moves the result the most. The historical average real return of the global equity market is around 5–7% per year after inflation — but in any specific 30-year window it could be higher or lower. A conservative calculation using 5% is a more sensible starting point than an optimistic 10%.
How to Refine the Calculation
The best tool is the Hřivna projection, which shows you a probability range of outcomes — optimistic, median, and pessimistic scenarios. This lets you see what could happen in an adverse case, not only what you expect on average. Update the calculation once a year using the current portfolio value and remaining time horizon — the plan becomes more precise over time.
FAQ
How much should I save monthly for retirement?
It depends on your target portfolio, time horizon, and return. The general rule: the earlier you start, the less you need to save each month. With a 30-year horizon and 6% return you need roughly half of what you would need with a 20-year horizon. Try the Hřivna projection tool.
What return should I assume in the calculation?
A conservative approach uses 5–6% per year in real terms (after inflation) for a globally diversified equity portfolio. Optimistic figures of 8–10% are historically possible, but they are too generous for lifelong financial planning.
What is compound interest and why does it matter?
Compound interest means that returns each year are earned not only on your contributions, but also on all earlier gains. After 30 years this produces exponential growth — even a small monthly contribution turns into a substantial sum. That is why time is the most valuable resource in investing.
Should I account for inflation?
Yes. If you are planning income 30 years from now, you must recognize that CZK 40,000 today will have different purchasing power in the future. Either work with the real return (return minus inflation), or index your target portfolio for inflation in the calculation.