Two actions per period
First add this period's contribution to the balance; then multiply the combined amount by (1 + rate per period).
Repeat for each period. The calculator on this site iterates in exactly that order — contribution first, growth second.
Formulas
(previous balance + contribution) × (1 + rate per period)principal × (1 + r)^n + contribution × (1 + r) × [(1 + r)^n − 1] ÷ rprincipal + contribution × periodsclosing balance − total contributedtotal gain ÷ total contributed × 100%Worked example (recompute it yourself)
Principal 1,000 USDT, 100 USDT added monthly, 1% monthly rate, 12 periods:
Principal part = 1,000 × 1.01^12 ≈ 1,126.83 USDT. Contribution part = 100 × 1.01 × (1.01^12 − 1) ÷ 0.01 ≈ 1,280.93 USDT. Closing balance ≈ 2,407.76 USDT.
Total contributed = 1,000 + 100 × 12 = 2,200 USDT, so the gain is about 207.76 USDT — an overall return of roughly +9.44%.
The contribution part ends at 1,280.93 against 1,200 contributed; the difference is interest earned period by period.
Risk notice (please read)
The monthly rate in the example is a calculator input. No strategy is promised to hold that rate, and it is not a return promise.
Contributions also enlarge the position: if prices fall, a larger amount invested means a larger nominal loss.
Real results depend on market moves, fees, slippage and liquidity, and the principal can lose value.
FAQ
Is the contribution added at the start or the end of a period?
At the start: the calculator adds the contribution to the balance, then applies the rate to the whole amount. Adding it at the end produces a slightly lower result.
Why iterate if there is a closed-form formula?
The closed form only holds when both the contribution and the rate stay constant. If either changes period to period, you have to iterate.
Is this the same as DCA?
The bookkeeping is the same — a fixed amount per period. The difference is that here each period grows at an assumed rate, while DCA converts through an actual price path.