Mintelo · Free Calculator
Time-Weighted Return Calculator
How TWR is computed
The honest figure, and the misleading one
Most people judge an investment by dividing total profit by what they put in, or worse, by comparing the ending balance to the starting balance. Both break the moment money moves in or out part-way through.
Time-Weighted Return removes the effect of contribution timing. The period is split at each cash flow; each sub-period's return is calculated on its own, then the sub-periods are geometrically linked — that is, the growth factors (1 + each sub-period's return) are multiplied together. (This is the standard method in the CFA curriculum and the GIPS performance-measurement standards.)
TWR = (1 + r₁) × (1 + r₂) × … × (1 + rₙ) − 1
where rᵢ = (value before flowᵢ ÷ value after previous flow) − 1
The result is the return a single unit of currency (one rand) would have earned if it had stayed invested for the whole period — the figure you can fairly compare against an index or another portfolio, regardless of when you happened to contribute.
Worked example
Start R1 000 000. After six months it's worth R1 060 000; you then contribute R200 000. By year-end it's R1 300 000.
Sub-period 1: 1 060 000 / 1 000 000 − 1 = +6.00%
Sub-period 2: 1 300 000 / 1 260 000 − 1 = +3.17%
TWR = 1.06 × 1.0317 − 1 = +9.37%
The naive "profit ÷ invested" reads +8.33% (100 000 ÷ 1 200 000). The truly wrong "end ÷ start" reads +30.00% (1 300 000 ÷ 1 000 000 − 1) — it credits your R200 000 contribution as investment growth. TWR is the only one of the three you can put next to the JSE All Share and compare honestly.
Simple vs Advanced: which method runs
The Advanced tab computes true Time-Weighted Return: you supply the portfolio value on each date money moved, the timeline is split at each flow, and the sub-period returns are geometrically linked. It is exact because you provide the interim valuations.
The Simple tab is for when you only know your starting balance, a regular contribution, the period, and the ending balance — with no interim valuations. It uses the Modified Dietz method, the standard way to approximate a return when you don't have a valuation at every cash-flow date. It is marked approx. because it estimates rather than measures the timing effect; for smooth returns the two agree closely, and they can diverge when a large contribution lands just before a sharp market move.
How do I calculate my investment return with monthly contributions?
Use the Simple tab: enter your starting balance, your monthly contribution (or switch to annual deposits), the period, and your ending balance. The calculator returns a time-weighted return with contributions factored out, so the figure reflects performance rather than how much you added.
Money-weighted vs time-weighted return — why is my brokerage's number different?
Most platforms headline a money-weighted return, which is influenced by when you deposited. A time-weighted return removes that timing effect, so you can compare like-for-like against an index or another investor. The two diverge most when a large deposit lands just before a sharp market move.
Does this work for withdrawals too?
Yes. Enter a negative amount for a net withdrawal in either tab. The method handles money flowing out exactly as it handles money flowing in.
Do my numbers leave my computer?
No. Every calculation runs in your browser. Nothing is uploaded, stored, or sent to a server — which also keeps it clean under POPIA.