Modified Dietz Return Calculator
Your personal rate of return over a period with dated deposits and withdrawals, by the Modified Dietz method, beside the plain end-over-start figure that ignores them.
Result
Modified Dietz return for the period: 12.233%
An approximation of the money-weighted return. It assumes growth was even through the period, so a large flow in a volatile month can move the answer.
- Annualised
- 12.233%
- End ÷ start, ignoring the flows
- 18%
- Investment gain
- $13,000.00
- Net deposits
- $5,000.00
- Average capital invested
- $106,273.97
- Days in the period
- 365
https://calcgallery.com/investment-returns/modified-dietz-return-calculator/
Results are arithmetic on the returns, rates and horizons you enter, not a forecast and not investment, tax or retirement advice. The site supplies no expected return, inflation rate, contribution limit, tax rate or withdrawal rate. Real returns vary from year to year, and fees, taxes and the order of returns all change the outcome. Check anything that matters with a qualified adviser. Read the full disclaimer
How to use the Modified Dietz Return Calculator
- Enter the first and last dates of the period you want to measure, such as a calendar year.
- Enter the account's value on each of those dates, from your statements.
- Add a row for every deposit and withdrawal in between, with its date. A withdrawal is a minus amount.
- Read the return for the period, the annualised figure when the period is a year or longer, and the naive end-over-start figure beside it.
The formula
gain = end value − start value − Σ flowsweight of a flow w = (days in period − days from start to flow) ÷ days in periodaverage capital = start value + Σ (flow × w)return R = gain ÷ average capitalannualised (1 + R)^(365 ÷ days) − 1 (periods of a year or more)This is the form in the CFA Institute’s Guidance Statement on Calculation Methodology for the GIPS standards, which treats each flow as happening at the end of its day. A deposit on the first day counts almost fully; one on the last day counts not at all, because it had no time to earn anything.
Money-weighted, by design
The weight is what makes this your return rather than the market’s. A deposit made in the first week carries almost its full amount into the average capital; one made in the last week barely moves it. So the same gain divided by a larger or smaller average gives a lower or higher percentage depending on when the money arrived. That is the right answer to “how did my account do”, and the wrong one for judging a fund manager who had no say in the timing.
Getting the inputs right
- Use values on the exact start and end dates, not month-end balances a few days out. The page counts calendar days between them.
- Enter transfers between your own accounts as flows on both, out of one and into the other.
- Fees charged by the account and taken from it are part of the return, not flows. A fee paid from a bank account outside is not in the account at all.
- A flow dated outside the period is left out and the note says how many were.
What the diagram shows
The start and end values as bars at either end of a timeline, and each flow as a stroke up for a deposit or down for a withdrawal at its date. The closer a stroke sits to the start, the more of the period it counts for.
With your numbers
- Gain = $118,000.00 − $100,000.00 − $5,000.00 net deposits = $13,000.00
- Average capital = $100,000.00 + $10,000.00 × 0.7534 (Apr 1, 2025) + -$5,000.00 × 0.2521 (Oct 1, 2025) = $106,273.97, each flow weighted by the share of the 365 days it was invested
- Return = $13,000.00 ÷ $106,273.97 = 12.233%
Quick reference
An approximation of the money-weighted return. It assumes growth was even through the period, so a large flow in a volatile month can move the answer.
| Example | Modified Dietz return for the period |
|---|---|
| One year, a deposit in April and a withdrawal in October | 12.233% |
| Six months, deposits on the first and last day | 6.364% |
| Three years of yearly contributions | 47.735% |
| No flows at all | 7.5% |
| Monthly 500 into a 401(k), one quarter | 2.329% |
| A year with a large withdrawal | 5.897% |
Common questions about the Modified Dietz Return Calculator
- Why not just divide the end value by the start value?
- Because deposits are not investment gains. An account that starts at 100,000, receives 10,000 of new money and ends at 118,000 grew 18% by that division, but only 8,000 of the change came from the investments. The naive figure is shown so you can see how far off it is.
- Is this the same as my fund's published return?
- No. A fund reports a time-weighted return, which removes the effect of when money comes and goes, because the manager does not control that. The Modified Dietz figure is money-weighted: it reflects your timing, so adding money just before a fall lowers it. It is the one that answers how your own money did.
- How accurate is the Modified Dietz method?
- It is an approximation of the internal rate of return that assumes the account grew evenly across the period. It is close when flows are small next to the balance or markets were calm. With a very large flow in a volatile stretch, splitting the period at that date and linking the pieces gives a better answer; the GIPS standards ask investment firms to do exactly that for large flows.
- Why is there no annualised figure for a short period?
- A three-month return of 3% compounded as if it lasted a year reads as about 12.6%, a number the account never earned. The GIPS standards say returns for periods under one year must not be annualised, and the page follows that.
- Do reinvested dividends count as deposits?
- No. Dividends and interest paid into the account and kept there are part of the return. Only money that crosses the boundary of the account counts: contributions, transfers in and out, and withdrawals.