What could monthly investing
grow into over time?

Not every monthly contribution is invested for a full year

Initial capital is invested from the start; monthly contributions arrive at each month-end. Over one year, the first contribution grows for 11 months, while the twelfth arrives at the end and earns no return within that period. A plan funded at the start of each month produces a different result.

The examples below start with zero initial capital and add 100 monetary units monthly for one year. Total contributions are 1,200 in every case. The annual input divided by 12 is applied as a constant monthly rate, excluding taxes, fees and currency changes. Amounts are shown to two decimal places.

An annual input of 12% does not generate 144, or 12% of the contributed 1,200. The money arrives at different times. The displayed total return divides investment gain by total contributions; it is not the annual input or a cash-flow return such as XIRR.

Identify whether contributions or growth fund your target

Ending assets equal initial capital plus monthly contributions plus investment gain. Even the 0% example grows from zero to 1,200, but its investment gain is zero. Treating all balance growth after increasing contributions as performance can hide the saving effort required to reach a target.

First use 0% to see what contributions alone provide, then change either the monthly contribution or the term while holding other inputs constant. Next compare a lower return assumption with the target to distinguish the effect of funding from the effect of returns.

A constant-rate curve does not show real drawdowns

This simulation assumes the same return every month. It divides the annual input by 12 and compounds monthly, so the effective growth over 12 months can differ from that annual input. For example, a 12% input means 1% monthly, giving about 12.68% growth on money invested for the entire year.

The input range is 0–100%, so this tool does not model negative returns. The 0% result is therefore not a lower bound for actual investing. Markets can fall below contributed capital, and paused contributions or withdrawals also change outcomes. Use the investment backtest to examine contributions alongside historical price changes.

Existing cash and new monthly income call for different models

Money newly available from monthly income belongs in the monthly contribution field. If an existing lump sum will be invested in stages, compare the same starting budget including waiting cash. Entering that lump sum as both initial capital and monthly contributions counts the same money twice.

Compare lump-sum and phased investing with the same budget · Backtest monthly contributions using historical prices · Calculate monthly contributions for a target

Contribution timing

The initial amount is invested from the start, and each monthly contribution is added at month-end.

What the estimate excludes

The monthly return is held constant. Market volatility, taxes, and fees are not included.

Investing $500 monthly with no initial investment

This example uses an 8% annual return and month-end contributions for 10 years.

Total contributions

$60,000

Estimated value

$91,473

Estimated growth

$31,473

Later contributions have less time to grow than earlier contributions, so contribution timing affects how much of the final value comes from growth.

Frequently asked questions