£100 vs £200 Monthly
How much can regular saving really grow?
What happens when you save twice as much every month? Let's use numbers, percentages and a little mathematical thinking to find out.
- 💡 The Big Idea
- 🏦 A Real-Life Savings Example
- ⚡ Rate Race: £100 vs £200 Monthly
- 💷 Where Does the Extra Money Come From?
- 🧠 What Does FV Mean?
- 🎯 Grade 8–9 Challenge
- 🌱 Remember
💡 The Big Idea
Saving more each month gives your money more opportunity to grow. But don't assume that the final amount is simply the money you paid in.
When savings earn compound interest, interest is added to your balance, and that balance can then earn more interest.
The interesting question is: how much of the final balance came from you, and how much came from interest?
🏦 A Real-Life Savings Example
🧑 Saver A: £100 every month
🧑 Saver B: £200 every month
Both save for 10 years and both earn 5% annual interest, compounded monthly.
Before looking at the answer, make a prediction:
❓ If Saver B saves twice as much each month, will the final balance also be exactly twice as large?
Saving Race: £100 vs £200 Monthly
Move the sliders. Don't just watch the answer — look for patterns.
Compare the two monthly saving plans.
| Monthly saving | Paid in over 10 years | Value after 10 years* |
|---|---|---|
| £50 | £6,000 | £7,764.43 |
| £100 | £12,000 | £15,528.86 |
| £200 | £24,000 | £31,057.72 |
*Assuming 5% annual interest, compounded monthly, with payments made at the end of each month.
💷 Where Does the Extra Money Come From?
Let's look at Saver A.
£100 × 12 × 10 = £12,000
That's the amount Saver A actually puts into the account.
But after 10 years, the account has grown to about:
£15,529
So approximately:
£15,529 − £12,000 = £3,529
came from the interest earned over time.
🧠 What Does FV Mean?
FV = Future Value
It simply means:
“How much will my money be worth in the future?”
In financial mathematics, you may see FV used as shorthand for the final value of an investment or savings plan.
You don't need to memorise a complicated formula here. The important mathematical idea is understanding how percentage growth, repeated payments and time interact.
🎯 Grade 8–9 Challenge
1. What percentage of Saver A's final balance came from interest?
Use:
Interest ÷ Final Value × 100
Use £3,529 and £15,529, then round your answer to 1 decimal place.
2. What percentage of Saver A's final balance came from the money they personally paid in?
3. Think carefully: If the interest rate changed from 5% to 6%, would the final balance increase by exactly 20%?
Explain why or why not. Don't just calculate — think about what the percentage change actually means.
🌱 Remember
Regular saving + time + compound interest can turn repeated small payments into a much larger balance.
For Grade 8–9 thinking, don't stop at the final number. Ask:
Where did the number come from? What percentage changed? What assumptions are we making?
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