Irish Calculators
Saving & investing

Compound Interest and Savings Growth Calculator

Estimate a future balance from a starting amount, regular contributions and a chosen return. Rates are scenarios, and the optional tax input is only a charge on positive growth at the end.

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Your numbers

%
A scenario, including price growth where relevant.
%
Applied as a proportional reduction over each period.
%
Used only for purchasing-power values.
%
Scenario deduction at the end only; not DIRT or another statutory assessment.
Display currency only. Convert all inputs to this currency before calculation.
Your figures stay on this device.

How the calculation works

This projection follows a starting balance and regular non-negative contributions through equal periods. It separates money paid in, modelled growth, fees and purchasing power, while allowing several ways of quoting the annual growth assumption.

Convert the declared rate to an effective annual rate. Grow each period’s balance, apply the proportional fee, and add the scheduled contribution at its chosen timing. Deflate by (1+inflation)^years.

  1. Convert the annual growth assumption

    The chosen convention is converted into effective annual growth, then into growth for each contribution period. Compounding frequency and contribution frequency serve different roles.

  2. Follow the balance through each period

    Beginning contributions are added before growth; end contributions follow it. Proportional balance charges are deducted during the projection, so they also reduce later growth.

  3. Separate nominal and real results

    The final balance and paid-in total identify modelled net growth. Dividing the balance by accumulated inflation shows its value in today's money, while the optional final tax adjustment is shown separately.

Worked example: Check Final balance

Sample inputs demonstrate the method. They are not a forecast or product offer.

The first example starts at 1,000 with no contributions, fees, inflation or tax. Two years at 10% effective annual growth produce 1,100 after one year and a final balance of 1,210.

Starting balance
1000
Contribution per period
0
Annual effective growth rate (%)
10
Years
2
Periods per year
Annual
Contribution timing
End of each period
Annual balance fee (%)
0
Annual inflation (%)
0
Rate convention
Annual effective (AER/APY)
Compounds per year for a nominal rate
1
Assumed tax on positive final growth (%)
0
Currency for all amounts
Euro (EUR)

Expected result

Final balance
€1,210.00
Worked example: Check Final balance

Sample inputs demonstrate the method. They are not a forecast or product offer.

Starting balance
0
Contribution per period
100
Annual effective growth rate (%)
0
Years
1
Periods per year
Monthly
Contribution timing
End of each period
Annual balance fee (%)
0
Annual inflation (%)
0
Rate convention
Annual effective (AER/APY)
Compounds per year for a nominal rate
12
Assumed tax on positive final growth (%)
0
Currency for all amounts
Euro (EUR)

Expected result

Final balance
€1,200.00

Understanding your result

A larger final balance can result from more contributions rather than a higher return. Compare the paid-in amount alongside the growth figure to distinguish those effects.

The chart follows a constant scenario rather than historical market prices or a bank's daily statement calendar. A displayed currency does not provide product rates or foreign-exchange conversion.

Questions you might have

What does the result include?

Project savings or investment growth with regular deposits, compounding, fees and inflation.

Which limits should I check?

The form accepts non-negative contributions. Contribution periods use equal fractions of a year; no bank-specific daily accrual calendar.

Choosing the right inputs

Contribution per period
Enter an amount added each contribution period, or zero. The current form does not accept withdrawals, even though some related financial models do.
Rate convention
Identify whether the entered rate is effective, nominal or continuous. For a nominal quote, also supply its compounding count.
Assumed tax on positive final growth
The optional percentage applies only to positive net growth at the horizon. It is not periodic withholding or a calculation of DIRT or another legal liability.

Common mistakes to avoid

  • Do not deduct the same fee in both the return assumption and balance-fee field.
  • Choose a horizon with a whole number of contribution periods.

Assumptions to check

  • The form accepts non-negative contributions. Contribution periods use equal fractions of a year; no bank-specific daily accrual calendar.
  • All calculations run on your device. Figures are scenarios based on your inputs, not investment recommendations.

Sources and method

Read our calculation and testing approach.