Mutual fund savings plan calculator

What the mutual fund calculator is actually doing

A savings plan calculator is a projection tool. It takes the amount you say you will put in each month, the number of years you say you will keep saving, and a yearly rate you supply, then shows how those regular contributions add up over the chosen period once the rate is applied to the running balance. The engine compounds the balance as time passes and adds each new monthly contribution to it. Two figures come back: the total you paid in, and the extra amount the rate produced on top of your contributions. Nothing more is being calculated than that.

The rate field arrives pre-filled with the central bank policy rate. That figure is a policy tool set by the central bank, not the return of any mutual fund and not a forecast of one. It sits in the field as a starting number you may replace, and whatever you type there is treated as a steady rate applied without variation across the whole period. A real fund does not earn the same rate every year: its holdings change in value and its return varies from one period to the next. The steady rate is a simplifying assumption, and the output is an illustration of what a given pattern of contributions and a constant rate would produce, not a statement of what you will receive.

Read the two figures with that in mind. The contribution total is arithmetic on your own inputs. The growth figure depends entirely on the rate you entered, so it moves whenever you change that field, and it is not evidence about any fund's behaviour. The result also leaves things out: it does not subtract fund fees or charges, it does not subtract tax, and it ignores movements in the price of the fund's holdings. Use the output as a rough guide for planning only, and check a fund's own documents for its fees and its past returns, remembering that past returns do not predict future ones.

Reading the input fields and the two figures it returns

The first field asks for the amount you plan to put in each month. Type the figure you can actually set aside on a repeating basis, not the amount you hope to manage in a good month. The engine treats that entry as a fixed instalment, so a figure you cannot sustain will flatter the output. The second field takes the number of years you intend to keep saving. This is your own saving horizon, not a feature of any fund, and changing it shifts both outputs because more instalments are counted and the balance has longer to compound.

The third field is the yearly rate applied to the running balance. It arrives pre-filled with the central bank policy rate, which is a policy tool and not the return of any mutual fund. You may overwrite it to test an assumption of your own. Whatever you type there is held constant for the whole period, so the field is a modelling choice rather than a reading taken from a fund's records.

Two figures come back. The first is the total you paid in: the monthly amount multiplied by the number of months in your chosen term. The second is the extra amount the rate produced on top of those contributions, after the balance is compounded and each new instalment is added. Read them together, because the first figure is money you supplied and the second is the part that depends entirely on the rate you typed.

The monthly amount is an instalment, not a target balance.

The years field sets how many instalments are counted.

The rate field is an assumption you control, pre-filled from policy.

The paid-in figure ignores growth; the extra figure ignores your deposits.

Why the pre-filled rate is not a fund return

The figure already sitting in the rate field is the central bank policy rate. It is a policy tool that the central bank sets and uses to steer conditions in the economy. It is not the return of any mutual fund, and it is not a forecast of one. The field is filled this way because the engine needs some number to run the compounding, and the policy rate is a familiar public reference rather than a figure tied to any particular fund.

Treat the pre-filled figure as a placeholder you are free to replace. A mutual fund's return comes from the change in value of what the fund holds, less its fees and charges, and that path varies from period to period. The policy rate does not describe that path. If you leave the field unchanged, the output tells you what a steady rate of that size would produce on your contributions; it says nothing about what any fund would pay. You can enter a different rate to test how sensitive the result is to the assumption, but any rate you type is still an assumption, not a projection.

Before relying on a figure of your own, check with the provider:

whether the fund publishes a stated return history and over what periods;

which fees and charges are deducted, and when;

how often the fund's holdings are valued and the return reported.

Those documents describe the fund itself. The pre-filled policy rate does not.

What the projection leaves out and why real funds vary

The projection you see is a gross illustration. It does not subtract the fees and charges a fund applies, and it does not subtract tax. Charges can be taken as a management fee, as a charge when you buy or sell units, or as a share of the fund’s assets deducted before a unit price is published. Each of these reduces what an investor keeps, and they are applied by the provider in its own way. Tax treatment depends on the type of account and on the rules in force, and it is not modelled in the output at all.

The figures also ignore movement in the price of the fund’s holdings. A mutual fund holds securities whose market values rise and fall as markets and conditions change. The calculator treats the balance as if it grew smoothly, but a real fund’s value per unit is recalculated as its holdings are repriced, so the value of a holding can be lower at the point you sell than at the point you bought. A steady rate is a simplifying assumption, not a description of how a fund behaves.

A real fund does not earn the same rate every year. Its holdings change in value, its mix may change, and its return varies from one period to the next, including periods of loss. When you read a projection, treat the two figures as a rough planning guide. Then check the fund’s own documents for its fee schedule, its charges, its tax position and its past returns, remembering that past returns do not predict future ones.

Questions to take to the provider before you rely on the output

Before relying on the projection, request the fund's own documents and read them alongside the figures the calculator produced. The documents should describe the fees and charges that apply, including any entry or exit charges, a management fee and other ongoing costs. Check how each charge is taken and whether it is deducted from the fund's assets or billed separately, since this affects how the figures you see in the calculator would differ from what a fund actually delivers.

Request the fund's past returns as well, and look at how they were calculated and over which periods. Remember that past returns do not predict future ones. A steady rate in a calculator is only a simplifying assumption, and the output is a rough guide for planning rather than a statement of what you will receive. Treat the projection as a starting point for questions, not as an answer.

When you speak with the provider, put these questions to them:

Which fees and charges apply, and how and when are they deducted?

How have the fund's returns been calculated, and over which periods?

What does the fund's documentation say about how its holdings are valued and how often?

What happens to the plan if contributions are missed or the saving period is shortened?

Record the answers and compare them with what the calculator assumed, so you understand where the projection and the fund's own documents differ.