This is an equity investment without any withdrawals so the rate of return would be compounded. Also, yes, monthly contributions are made at the beginning of each month [....] Does that change anything?

Yes. I explained all the necessary changes in my previous suggestions. To summarize (referring to my example):

=FV(C4, B3, -B6-FV(B4, 12, -B5, 0

**, 1**), -B2)

or if you prefer Dave's form (in the context of my example):

=FV(B4, B3*12, -B5, -B2

**, 1**) + FV(C4, B3, -B6, 0)

It is the addition of the 5th parameter ("type") for FV and setting it to 1 for (only) the calculation of the monthly contribution that makes the difference.

Also, to check with my amortization schedule, H3 should be:

=(H2

**+F3**)*(1+$B$4) + N(G3)

In other words, the monthly contribution is added to the previous balance, then monthly interest is applied.

Finally, to reiterate, if the rate of return is specified as an annual rate in C4, the monthly rate in B4 is =(1+C4)^(1/12) - 1, not B4/12.

OTOH, if the rate of return is specified as a monthly rate in B4, the annual rate in C4 is =(1+B4)^12 - 1, ,as shown in my example. It is not B4*12.

but the bonus is actually contributed in March (not at end of year).

The "year" should be 12 months starting with April. Thus, the bonus is indeed at the end of "the year" (12-month period).

If you cannot align your annual cash flows with April, then we must adjust the formulas to include "odd periods": first and/or last.

In order to assist you with that, we need more information. Provide the following dates:

1. First and last monthly contribution

2. First and last annual bonus

3. First and last date of the annuity, if that does not align with #1 or #2 (!)