🏦 Savings Calculator
Project your savings balance including regular monthly contributions and compound interest growth.
Enter Your Values
How Compound Growth Turns Regular Savings into Significant Wealth
This calculator uses the future value of an annuity formula: FV = P × (1 + r)^n + PMT × [((1 + r)^n − 1) ÷ r], where P is your current balance, r is the monthly interest rate, n is the number of months, and PMT is your monthly contribution. Compound growth means you earn interest not only on your contributions but on the interest you've already earned — this is the mechanism that causes wealth to accelerate over time rather than grow linearly.
The time value of money is the most important concept in personal finance. A rand saved today is worth more than a rand saved ten years from now because today's rand has more time to grow. This is why starting to save as early as possible — even small amounts — produces dramatically better outcomes than saving larger amounts later. Starting to save $500 per month at age 25 and stopping at 35 (10 years of contributions) will typically produce a larger retirement balance by age 65 than starting at $500/month at 35 and continuing for 30 years — because of the additional 30 years of compound growth on the early contributions.
Realistic return expectations for savers: cash (savings accounts, money market) currently earns 7–9% per annum. Fixed deposits are similar. SA government bonds yield approximately 10–12% for longer-term instruments. Balanced unit trust funds have historically returned approximately 10–12% nominally over 10+ year periods. Equity-only funds (like the JSE All Share Index) have historically returned approximately 12–16% annually over long periods but with significant year-to-year volatility. After inflation (currently 4–7%), real returns are meaningfully lower than nominal rates — a key reason to use nominal rates in this calculator rather than a real rate.
The small difference a higher return makes over time is striking. $1,000 per month over 20 years: at 6%, the balance reaches approximately $462,000. At 8%, $589,000. At 10%, $765,000. At 12%, $988,000. The difference between a 6% and 12% return is more than doubling the outcome over 20 years. This is why investment return matters enormously for long-term financial outcomes, and why keeping costs (fund management fees, platform fees) low is so important.
How to Calculate Savings Growth
Savings growth combines two components: interest on your starting balance (compound growth) and the future value of regular contributions. The formula is: FV = P × (1 + r)^n + PMT × [((1 + r)^n − 1) ÷ r], where P is the starting balance, r is the monthly interest rate, n is months, and PMT is monthly contribution.
The most powerful lever in savings growth is time, not rate. Starting 10 years earlier typically has more impact than doubling your interest rate. Even small regular contributions compound significantly over decades — the key is starting and automating before the habit can be skipped.