Compound savings scenarios
Initial capital, regular deposits and two own rates per interval.
- Runs in your browser
- No upload
- Check before download
Initial capital, regular deposits and two own rates per interval. Choose deposits at the beginning or end of each interval; contributions and rounded interest are shown separately.
Calculations run locally and inputs are not saved automatically. Download an input backup before closing the tab. Input data, formulas and filenames are never sent. Only with your optional consent, Refentra sends aggregate counts of actions and outcomes, without input content.
What are the limits?
Maximum amount 1 trillion units; total 100 trillion cents. Up to 100 rows, 50 people, 20 tiers, 100 depreciation years, 1,200 schedule periods, 61 cash flows. IRR range −99% to 1,000% per interval, numerical candidates only. Rates: up to eight decimals. Backup: 1 MiB. CSV formula-leading text gets an apostrophe. Use decimal points, no thousands separators.
Amounts use two decimals in your stated unit. Exact decimal inputs; cent rounding half away from zero. Table sums balance. Largest fractional remainders receive shared cents; equal remainders use row order. No tax, fees, legal entitlement or current prices are inferred.
Non-monetary values are shown with up to ten significant digits. CAGR, fractional-year inflation and IRR use numerical approximations; IRR candidates are not a symbolic proof. CSV keeps the numeric values before display rounding.
I_t = round((B_(t−1)+D_start)×r); B_t = B_(t−1)+D+I_t
Calculate with your own assumptions
- Enter the inputs
Enter the starting balance, the contribution, the number of periods, two rates and the deposit timing. The rate applies per month or year, as selected, and is not annualized automatically. With start timing, that period’s deposit earns interest; with end timing, it doesn't. Enter decimals with a point and without thousands separators.
- Check a worked example
Start 100, deposit 10, two months, rate 1% per month, end timing: 100+1+10=111; 111+1.11+10=122.11. The 0% comparison ends at 120. Start timing instead ends at 122.31.
- Interpret and save the result
Interest is rounded to cents in every period before the balance is updated. Contributions do not include the initial balance. Compare the final balances and the interest separately. Export both scenario schedules as CSV.
Method, errors and limits
Can I reopen editable inputs from the CSV?
The CSV is a report of the results, not a backup of your inputs. Download the separate JSON input backup before you close the page, then import it into this same tool to edit your assumptions again. Import accepts files up to 1 MiB and checks that the file belongs to this tool. Inputs are not saved automatically.
Which input mistakes should I check?
Periods must be a whole number from 1 to 1200, and each rate must be between −99% and 1000%. Enter 1 for 1%, not 0.01. If you enter an annual 1% rate in monthly mode, it becomes 1% each month and changes the model.
What are this model’s limits?
Two illustrative scenarios with constant rates, without tax, fees, withdrawals, market ups and downs or guaranteed returns. Very large balances beyond the money limits are rejected.