Savings Growth (Variable Monthly Contributions)

Calculate savings growth when monthly contributions change each year

This calculator estimates how your savings balance could grow over time when you deposit money monthly and your monthly deposit changes from year to year. The most common real-world case is a “step-up” plan where you increase your monthly contribution each year (for example, after a salary increase). It also supports a decrease, as long as the change rate does not push the contribution below zero.

The primary decision this page supports is simple: if you start saving now and adjust your monthly contribution annually, what balance might you reach by a target year. The result is meant to help you choose a starting monthly amount and a realistic yearly change rate, then see whether the outcome is in the right ballpark. It is not designed to price investment products, compare tax treatments, or optimize retirement withdrawals. It is strictly a savings growth projection with monthly compounding and annually changing monthly deposits.

To use it, enter your starting balance (you can use 0 if you are starting from scratch), your monthly contribution for the first year, and an annual contribution change percentage. For example, a 6% annual contribution change means your monthly deposit increases by 6% at the start of each new year. Then enter an annual interest rate and your time horizon in years. The calculator will show your projected ending balance, how much you contributed in total, and how much of the ending balance is estimated interest growth.

Assumptions and how to use this calculator

• Interest compounds monthly using the annual interest rate divided by 12 (this is a common planning approximation).
• Monthly contributions are added at the end of each month, after that month’s interest is applied.
• Your monthly contribution changes once per year (at the start of each new year), based on the annual contribution change percentage.
• Contribution change can be negative, but it must be greater than -100% so the contribution never becomes negative.
• This is a gross projection that ignores taxes, fees, inflation, and product-specific rules, so treat it as directional planning.

Common questions

What does “annual contribution change” mean in practice?

It means your monthly deposit is updated once per year. If you set it to 5%, and you contribute 2,000 per month in year 1, then year 2 becomes 2,100 per month, year 3 becomes 2,205 per month, and so on. The calculator applies the change at the start of each year and keeps contributions fixed for the 12 months of that year.

What if my contribution changes more often than once per year?

This calculator does not model month-by-month manual changes or irregular deposits. It is intentionally locked to a common planning pattern: a stable monthly deposit that steps up (or down) annually. If your contributions are irregular, you can approximate by using the average monthly amount for year 1 and a realistic annual change rate that reflects your expected trend.

Is the interest rate “guaranteed” in this calculation?

No. The annual interest rate is an assumption you provide. For a savings account, you might use a current quoted rate, but rates can change. For investments, returns vary year to year. Use a conservative rate for planning if the goal is to avoid overestimating your future balance. If you want a range, run the calculator multiple times with low and high rate assumptions.

Why can my “interest earned” look small in the early years?

Compounding is slower when balances are small. Early on, most of your growth comes from your contributions, not interest. Over time, as the balance grows, the interest component typically becomes more noticeable. That shift is normal and is one reason consistent saving matters.

What inputs make the biggest difference to the final balance?

Usually the time horizon and your contribution path. A modest annual step-up in contributions can materially change the outcome over long periods, especially when combined with compounding. The interest rate matters too, but relying on a high rate to “do the work” is risky. If you want a more reliable plan, focus on what you control: starting earlier and increasing contributions over time.