What return should I use?

That is your call, and it is only an assumption. A savings account pays a few percent; a broad stock index has averaged more over long periods, with years far below it. Try a few rates and watch how much the goal dates move.

Does it account for inflation?

Turn on today's money and every figure is shown at today's prices, with the inflation rate you choose taken out.

Monthly or yearly compounding?

Monthly, with the yearly rate spread so that a full year earns exactly what you set, and your addition going in each month.

Compound interest calculator

Start with what you have, add something every month and choose a yearly return. The route shows what it grows to, how much of it is growth rather than what you put in, and the month each goal arrives.

What you hold today

Currency

A summit to reach

Another summit

Nothing here is stored. Your route stays on this page while you use it and is forgotten on reload. A free account keeps it and lets you add your real figures. Starting amounts are planning assumptions, not financial records.

RouteYour route

Flags mark when this route reaches each summit.

$292,458

$500 a month · 7% · 20 years · by October 2046

2 to go

Summits ahead

Dates follow this route

Where it comes from

Growth does 56%

$292,458

Growth: $162,458
You add: $120,000
Today: $10,000

Today$57

Oct 2033$394

Oct 2039$841

Oct 2046$1,654

Independence number

See how much you need for everyday life

$750,000

0.3of 25 years covered

Monthly spending

Arrives: June 2058 on your route

Monthly spending × 12 ÷ withdrawal rate. Illustrative, not advice.

The formula

With a starting balance P, a monthly addition A and a monthly rate r, the balance after n months is:

P × (1 + r)ⁿ + A × ((1 + r)ⁿ − 1) ÷ r

Uphill takes r from the yearly return R as the twelfth root of (1 + R), minus one, so twelve months of growth make exactly R. Each addition goes in at the end of its month.

Why the curve bends upwards

Growth earns growth. In the first years most of the balance is what you added; later, what the money earns each month can overtake what you add. The growth per month card shows the month that happens.

Questions

What return should I use?: That is your call, and it is only an assumption. A savings account pays a few percent; a broad stock index has averaged more over long periods, with years far below it. Try a few rates and watch how much the goal dates move.
Does it account for inflation?: Turn on today's money and every figure is shown at today's prices, with the inflation rate you choose taken out.
Monthly or yearly compounding?: Monthly, with the yearly rate spread so that a full year earns exactly what you set, and your addition going in each month.