Mon Avise planner
Compound Interest Calculator
Use this free compound interest calculator to model regular contributions, investment fees, inflation, withdrawals and retirement income over time.
Calculator
Set your assumptions
Start with the core investment details. Your projection updates as you refine each value.
Projection
Your forecast
A summary of the current assumptions, followed by the projected balance over time.
Final Balance
Projected value at the end of the termInitial Investment
Added Contributions
Total Invested
Total Interest
Cost of Fees
Today's Value
Time-Weighted Return
Actual Annual Return (IRR)
Rate sensitivity
Forecast range
Conservative
Expected
Optimistic
Growth over time
Balance projection
Use the planning tools below to model future changes.
Planning tools
Refine your projection
Choose a tool, adjust the assumptions, and see the projection update.
One-off withdrawals
Add future cash needs such as a house deposit, education cost, or large purchase.
No one-off withdrawals added. Your balance remains fully invested.
Detailed view
Yearly breakdown
Review contributions, withdrawals, interest, and the closing balance for each year.
| Year | Contribution | Withdrawal | Interest | Fees | Accrued Interest | Balance |
|---|
Calculator guide
Plan beyond a basic compound interest estimate
Understand what the projection includes, which assumptions matter, and how to use the result responsibly.
Compound interest is the growth earned on your initial investment and on returns already added to your balance. Mon Avise helps you explore how that compounding can change when you make regular contributions, pay investment fees, account for inflation, or withdraw money later.
The calculator is designed for savings and investment planning rather than predicting a guaranteed outcome. Compare conservative, expected, and optimistic scenarios before making a financial decision.
Regular contributions
Model monthly, weekly, or yearly investing and choose whether contributions run for the full term or a selected range of years.
Fees and inflation
Include platform, fund, and fixed annual fees. Switch to today's money to see how inflation can affect future purchasing power.
Withdrawals and retirement
Add one-off cash needs or test inflation-adjusted retirement drawdown, depletion risk, income coverage, and an early market-fall scenario.
Financial goals
Track milestones such as an emergency fund, home deposit, education costs, or a retirement target alongside the main forecast.
How compound interest is calculated
For an initial amount without additional cash flows, the standard formula is:
A = P(1 + r / n)nt
P is the starting principal, r is the annual interest rate, n is the number of compounding periods per year, and t is the number of years. Mon Avise simulates each period so it can also include contributions, fees, withdrawals, and drawdown.
Methodology
Calculation assumptions and limitations
Understanding the model helps you interpret the result responsibly.
Returns and contributions
The selected annual rate is divided across your chosen compounding frequency. Regular contributions are added before interest is applied in each matching period and may increase yearly by your contribution inflation setting.
Fees and inflation
Platform and fund fee percentages are combined with any fixed annual fee and deducted after growth at the end of each year. Today's-money values discount each future year using your general inflation assumption.
Withdrawals and drawdown
One-off withdrawals and retirement drawdown are applied after yearly fees. Drawdown may rise annually with inflation. A withdrawal cannot reduce the modeled balance below zero.
Forecast ranges
Conservative and optimistic figures apply your selected variance below and above the expected annual rate. They are sensitivity illustrations, not probabilities. The early-fall test applies a one-off market reduction at drawdown start.
What the projection does not model
Real investment returns vary over time. The calculator does not model market volatility year by year, tax, product-specific rules, pension allowances, benefits, exchange-rate movements, or changes in your personal circumstances. Check the rules that apply to you before acting on a result.
Independent UK guidance
Read more before investing or planning retirement income:
Compound interest calculator FAQs
What is compound interest?
Compound interest is return earned on both the money you invest and the returns already added to your balance. Over a longer period, this can materially increase growth compared with simple interest.
Can I calculate compound interest with monthly contributions?
Yes. Set the contribution amount and choose monthly as the contribution frequency. You can also use weekly or yearly contributions and apply an annual contribution increase.
Why should I include investment fees?
Fees reduce the amount left invested and therefore reduce future compounding. Use the platform fee, fund fee, and fixed annual fee fields to create a more realistic projection.
What does today's money mean?
Today's money discounts future values using your inflation assumption. It helps you compare a future balance with the purchasing power of money today.
Can this calculator model retirement withdrawals?
Yes. Enable retirement drawdown to test annual income, inflation increases, projected depletion, income coverage, and an early market-fall stress scenario.
Is this financial advice?
No. The calculator provides illustrative projections. Actual investment returns, inflation, fees, taxes, and personal circumstances can differ from your assumptions.