Every financial goal reduces to the same question: how much per month, for how long? The answer changes character depending on the horizon — over short periods you are doing all the work, over long periods compounding does most of it.
For goals under about five years, growth barely helps. A £20,000 house deposit in four years is essentially £20,000 ÷ 48 months ≈ £420 a month; even in a decent savings account, interest contributes only a little on top. That is fine — for short-horizon goals the account is a holding pen, not an engine. Keep the money in cash or equivalents, because a badly timed 20% market drop the year you need the deposit is a risk with no compensating upside.
For long horizons, the picture inverts. As a rule of thumb at 7% annual growth, reaching £100,000 takes roughly £1,400 a month over 5 years, £580 over 10, £190 over 20, and £80 over 30. Read that again: the 30-year version costs less than a weekly takeaway. Time is doing almost all of the work — of the £100,000, less than £30,000 is money you actually put in.
The same logic explains why starting early beats saving hard. £500 a month for 30 years at 7% builds over £600,000, of which only £180,000 is contributions. Waiting ten years and saving £750 a month for 20 years contributes exactly the same £180,000 — but ends up around £390,000. The missing £220,000 is the price of the decade.
Match the vehicle to the horizon: cash for goals within five years, invested portfolios for goals beyond ten, and a judgement call — usually a blend — in between. As a long-horizon goal gets close, it gradually becomes a short-horizon goal, and its money should get more conservative to match.
Then automate it. A goal with a standing order attached is a plan; a goal without one is a wish. Set the transfer for payday, review the amount once a year, and let the boring machinery run.
If you want the numbers for your own goals rather than round examples: this is exactly what a growth projection is for. Set the target, the horizon, and a realistic return, and read off the monthly contribution — then argue with the assumptions, which is where all the interesting decisions live.