One calculator, three questions
Every savings plan is the same four quantities: what you start with, what you add each month, what it earns, and how long it runs. Pin any three and the fourth follows. This page solves the three versions people actually ask: how much a plan grows to, how long a goal takes, and what monthly deposit a goal demands. The interest arithmetic converts APY the way banks pay it, as (1 + APY)^(1/12) − 1 per month, never APY divided by 12, for reasons our HYSA calculator lays out in full.
Worked examples, one per question
How much will I have? $1,000 to start, $200 a month, 4.10% APY, five years: $14,490.68. Of that, $13,000 is your own deposits and $1,490.68 is interest.
When do I reach $10,000? Same start, same $200 a month: you cross the line in month 42, which is 3 years and 6 months. Without any interest it would take 45 months, so the rate buys back 3 of them.
What must I save monthly? $20,000 in three years, starting from $2,000 at 4.10%: $464.55 a month, landing on the goal to the dollar.
The honest split: the habit is the engine, the rate is the trim
Run $200 a month at 4.10% from zero and look at where the money comes from. After one year, interest has added 1.9% on top of your deposits. After five years, 10.6%. It takes about twenty years for interest to add half of what you contributed, and about thirty for it to roughly match your deposits dollar for dollar.
| Saving $200/mo at 4.10% | You put in | Interest | Interest as % of deposits |
|---|---|---|---|
| 1 year | $2,400 | $44.77 | 1.9% |
| 5 years | $12,000 | $1,268.17 | 10.6% |
| 10 years | $24,000 | $5,488.68 | 22.9% |
| 20 years | $48,000 | $25,560.67 | 53.3% |
| 30 years | $72,000 | $67,427.97 | 93.6% |
Both halves of that table are true and they answer different lives. At savings-account horizons, the deposit is nearly everything, which is liberating: a plan does not stall because rates dipped, and you do not need a perfect account to start. At retirement horizons, compounding becomes the main character, which is our compound interest calculator's territory. The mistake is applying either lesson at the other horizon: waiting to optimize the rate before starting a five-year plan, or trusting deposits alone to fund a thirty-year one.
What this page assumes, said out loud
Deposits land at the end of each month. The APY holds for the whole projection, which for a variable savings rate makes every multi-year figure an illustration at today's rate rather than a promise. Interest is taxable as ordinary income, so the real after-tax figure is smaller; our HYSA calculator prices that, along with what current high-yield rates actually pay and what staying at a low rate costs. And a goal with a fixed deadline that must not miss is a case for locking the rate, which is what CDs are for, priced on our CD ladder calculator.