Dream Come True Calculator
Set your dream price, current savings, expected annual rate and plan months to work out the monthly saving needed, and see how principal, contributions and interest compose the goal.
Input Data
Results
At a glance:The Dream Come True Calculator reverse-engineers the monthly saving for a wish goal (car, travel, home down payment...) using a compound-interest annuity: monthly contribution = (goal − principal × (1+r)^n) × r ÷ ((1+r)^n − 1), where r = annual rate ÷ 12 and n = plan months; when existing savings compounded already reach the goal, the contribution is 0. The result also splits 'existing principal', 'total contributions' and 'interest earned' so you see how much is your own saving versus compounding.
Formula
Monthly rate r = annual rate ÷ 12; months n = plan length.
Monthly contribution = (goal − principal × (1+r)^n) × r ÷ ((1+r)^n − 1).
Total contributions = monthly contribution × months; interest = goal − principal − total contributions.
$$PMT = \dfrac{(G - P_0 (1 + r)^n)\, r}{(1 + r)^n - 1},\quad r = \dfrac{annual\%}{12}$$$$Interest = G - P_0 - PMT \times n$$How to Use
- Enter the dream price (goal amount).
- Enter current savings, expected annual rate and plan months.
- Instantly get the monthly saving and the breakdown of principal, contributions and interest.
Dream HK$300,000, current HK$50,000, 4% p.a.: monthly saving and breakdown by plan length
| Plan months | Monthly saving (HK$) | Total contributions (HK$) | Interest earned (HK$) |
|---|---|---|---|
| 12 | 20,287 | 243,450 | 6,550 |
| 24 | 9,856 | 236,550 | 13,450 |
| 36 | 6,381 | 229,716 | 20,284 |
| 60 | 3,604 | 216,248 | 33,752 |
Case Studies
Case 1: save HK$300k down payment in 3 years
Goal HK$300,000 in 36 months, current HK$50,000, expected 4% p.a. monthly compounded.
Monthly rate r = 4% ÷ 12 ≈ 0.3333%; monthly saving ≈ HK$6,381; total contributions = 6,381 × 36 ≈ HK$229,716; interest = 300,000 − 50,000 − 229,716 ≈ HK$20,284.
About HK$6,381/month reaches the goal in 3 years; ~HK$20k of the HK$300k comes from compounding, the rest from your own saving.
Case 2: save HK$200k for travel in 2 years
Goal HK$200,000 in 24 months, current HK$20,000, expected 3%.
Monthly saving ≈ HK$7,237; total contributions ≈ HK$173,679; interest ≈ HK$6,321.
With a shorter horizon and lower rate, compounding covers only ~HK$6,321 — discipline does most of the work; start earlier or extend the horizon to ease it.
FAQ
If the monthly contribution is too high, what can I do?
Three options: extend the plan (more months → lower monthly), lower the dream price or stage it, or raise the expected rate (riskier). Extending time is usually the safest.
Is the rate guaranteed? Is the result accurate?
The model assumes a fixed annual rate compounded monthly; real returns fluctuate. Treat the result as planning reference and review periodically.
Why can the monthly contribution be 0?
When your existing savings compounded at the expected rate already reach or exceed the goal by maturity, no extra contribution is needed and the result shows 0 — you have effectively 'pre-qualified'; consider a more ambitious dream.
How much does plan length affect the monthly saving?
Time is the most powerful and overlooked variable — lengthening it sharply lowers the monthly burden because the goal spreads over more periods and compounding has longer to work.
How is interest earned computed? What does it mean?
Interest earned = goal − existing principal − total contributions. It is the part compounding earns for you, reducing what you must save — the most encouraging number here.
Related Tools
References
Content review: Calculatorism Finance Team. Results are for reference only; please refer to the relevant authorities for the official figures.