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You can use Tally’s calculated fields to build a basic simple-interest calculator in a form. Add numeric questions for principal, annual interest rate and time, then use a formula to calculate interest and—if needed—the total including principal. This is a user-built estimate, not a dedicated Tally interest-calculator feature or a substitute for a lender’s terms.
What this Tally calculator can—and cannot—do
Tally calculated fields perform arithmetic on answers and can display a result when you insert the calculated value into form text. The formula below calculates simple interest: it assumes the rate stays constant and does not compound. Tally’s documented operators include addition, subtraction, multiplication, division and parentheses; its documentation does not establish a built-in compound-interest or loan-amortization calculator. Tally’s calculated-fields guide
This walkthrough treats the annual rate as a whole percentage: enter 8 for 8%, not 0.08. It also uses a numeric duration in years. Tally states, “Calculations on date blocks are not available yet,” so do not subtract date-block answers to derive elapsed time. For an estimate, ask for duration as a number; if exact dates matter, calculate the duration elsewhere and pass a numeric value into the form. Tally’s formula and date-block guidance
Step 1: Add the input questions
- Create a Tally form and add three numeric questions: Principal, Annual rate (%) and Time (years).
- Use clear, consistent labels. Formula references are case-sensitive, so select the actual fields with the editor’s autocomplete rather than typing names from memory.
- Tell respondents how to enter the rate and duration. For example, specify that 8 means 8% per year and that time should be entered in years.
Step 2: Calculate simple interest
- After the input questions, type
/calculated fieldand add a calculated field named Interest. Choose a numeric value. - In the formula editor, type
@and select the Principal, Annual rate (%) and Time (years) fields from autocomplete. - Enter the expression
@Principal * @Annual rate (%) * @Time (years) / 100, replacing each reference with the field selected from autocomplete. The formula uses Tally’s documented arithmetic operators; the simple-interest expression is a user-created example, not a preset. Tally calculated fields
For a principal of 1,000, a rate entered as 8 and a duration of 2 years, this expression returns 160 in interest. That illustration assumes simple interest, a constant annual rate, no fees or compounding, and rate entry on a 0–100 scale.
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Step 3: Calculate the total, if you need it
- Add a second numeric calculated field after Interest, named Total amount.
- Use
@Principal + @Interest, selecting both references using autocomplete. Because this field depends on Interest, keep it after that field too.
With the example inputs above, the total is 1,160. Label it clearly as principal plus estimated simple interest, not as a guaranteed payoff or contract amount.
Step 4: Show the result to respondents
Calculated fields are hidden unless you explicitly mention their values in the form. In a text block, type @ and choose Interest or Total amount from the suggestions. Add explanatory wording so respondents know what the displayed figure represents. You can also place a calculated value on a completion page. Tally’s documentation also describes using a calculated field in a payment block’s price field; use that only when the amount and payment flow are appropriate for your form. Calculated fields · Payment guides
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Step 5: Check the form and its calculation
- Preview the form and enter known values, including zero, decimal inputs and values at the ends of the range you expect respondents to use.
- Confirm the displayed result matches the intended formula and that the rate is entered as a whole percent, not a decimal fraction.
- Check that each calculated field comes after the questions and calculated values it references. Tally evaluates fields from top to bottom.
- Test the published form as well as the editor preview. If a result unexpectedly appears as zero, check field placement, logic order and exact case-sensitive references. Tally’s calculated-fields troubleshooting guidance
Choose the right method for the calculation
| Need | Suitable approach | Important limit |
|---|---|---|
| Simple interest over a stated duration | Use the numeric fields and formula in this guide. | State the assumptions, rate scale and duration unit. |
| Duration between two dates | Calculate elapsed time outside Tally and provide a numeric duration, or ask for duration directly. | Tally says calculations on date blocks are not available yet. Source |
| Compound interest or an amortization/payment schedule | Use a separately validated calculation method or external calculator, then show the resulting value if suitable. | Tally’s cited formula documentation lists basic arithmetic operators and does not establish native compounding or amortization. Source |
| Different next steps depending on an answer | Use conditional logic to calculate or show/hide relevant blocks, and test each answer path. | When calculations and page jumps share a flow, Tally says calculations should precede page jumps. Conditional logic |
Keep the estimate clear and appropriately limited
- State whether the calculation is simple or compound, what rate and time units mean, and whether fees or other charges are excluded.
- Explain any rounding you apply. The cited documentation does not establish financial or legal disclosure standards, a day-count basis, taxes, fees or a rounding rule.
- Present the output as an estimate, not as a lender’s payoff quote, disclosure or contract amount. For a binding financial figure, use the applicable lender terms and calculation method.
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