Mortgage affordability calculator template

Free build guide: Mortgage affordability calculator for WordPress

This guide rebuilds the Mortgage affordability calculator from this site in Gravity Forms: 9 inputs, 4 live results and no submit button. Expect about 42 minutes by hand. The template above is the same form as an import file, and the bundle adds a PDF version of this guide with a screenshot of every setting, plus the stylesheet.

You will end up with:

• Home price you can afford
• Maximum loan
• Monthly housing budget
• Principal & interest at that loan

What you need

• Gravity Forms (any license) — Calculation fields are in core; the exponent in the payment factor needs GP Advanced Calculations.
• GP Advanced Calculations (Gravity Wiz) — Exponents, functions and date math in calculation fields. The formulas in this template use its syntax. Part of Gravity Perks; needs the Spellbook plugin active as well.

The formulas below use GP Advanced Calculations syntax: exponents, functions or date math that core calculation fields cannot do. Install and activate it, with its Spellbook parent plugin, before you start; without it every result shows 0.

1. Create the form

1. Go to Forms → New Form and name it Mortgage affordability.
2. In Form Settings → Form Layout, set the CSS Class Name to fo-email-results, and the button text to Email me these results.
3. Leave the form open in the editor; the fields come next.

2. Add the fields, in this order

Field IDs are assigned as you add fields. If yours come out differently, change the {Label:ID} references in the formulas to match your IDs. Settings not mentioned stay at their defaults.

1. Household income per year · Number · ID 1
Number Format Currency; Default Value 100000; Description “Gross, before tax, everyone on the loan.”; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed).

2. Other monthly debt payments · Number · ID 2
Number Format Currency; Default Value 500; Description “Car loans, student loans, card minimums, child support.”; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed).

3. Down payment · Number · ID 3
Number Format Currency; Default Value 40000; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed).

4. Lender limit (debt-to-income) · Drop Down · ID 8
Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed).

Choices (tick show values and enter each value):

• 36% of income (standard) — value 36 (selected by default)
• 43% (FHA, strong credit) — value 43
• 30% (comfortable) — value 30

5. Interest rate (%) · Number · ID 4
Number Format 9,999.99; Default Value 6.5; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed).

6. Term (years) · Number · ID 5
Number Format 9,999.99; Default Value 30; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed).

7. Property tax (% of price per year) · Number · ID 6
Number Format 9,999.99; Default Value 1.2; Description “0.3% to 2.5% by state; 1% is typical.”; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed).

8. Home insurance per year · Number · ID 7
Number Format Currency; Default Value 1500; Description “Add PMI here if you put down under 20%.”; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed).

9. Home price you can afford · Number · ID 9
Number Format Currency; Description “The most a lender would approve on these numbers. Buying below it leaves room for life.”; Custom CSS Class (Appearance tab) fo-result; tick Enable Calculation, Rounding 0.

if( {Rate:4} == 0 ):
( ( ( {Income:1} / 12 * {DTI:8} / 100 - {Debts:2} ) - {Down:3} * ( {Tax rate:6} / 1200 ) - {Insurance:7} / 12 ) / ( ( 1 / ( {Term:5} * 12 ) ) + ( {Tax rate:6} / 1200 ) ) ) + {Down:3}
else:
( ( ( {Income:1} / 12 * {DTI:8} / 100 - {Debts:2} ) - {Down:3} * ( {Tax rate:6} / 1200 ) - {Insurance:7} / 12 ) / ( ( ( {Rate:4} / 1200 ) / ( 1 - ( 1 + ( {Rate:4} / 1200 ) ) ^ ( 0 - ( {Term:5} * 12 ) ) ) ) + ( {Tax rate:6} / 1200 ) ) ) + {Down:3}
endif;

10. Maximum loan · Number · ID 10
Number Format Currency; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed); Custom CSS Class (Appearance tab) fo-result fo-result--sub; tick Enable Calculation, Rounding 0.

if( {Rate:4} == 0 ):
( ( ( {Income:1} / 12 * {DTI:8} / 100 - {Debts:2} ) - {Down:3} * ( {Tax rate:6} / 1200 ) - {Insurance:7} / 12 ) / ( ( 1 / ( {Term:5} * 12 ) ) + ( {Tax rate:6} / 1200 ) ) )
else:
( ( ( {Income:1} / 12 * {DTI:8} / 100 - {Debts:2} ) - {Down:3} * ( {Tax rate:6} / 1200 ) - {Insurance:7} / 12 ) / ( ( ( {Rate:4} / 1200 ) / ( 1 - ( 1 + ( {Rate:4} / 1200 ) ) ^ ( 0 - ( {Term:5} * 12 ) ) ) ) + ( {Tax rate:6} / 1200 ) ) )
endif;

11. Monthly housing budget · Number · ID 11
Number Format Currency; Description “Principal, interest, tax and insurance together, after your other debts.”; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed); Custom CSS Class (Appearance tab) fo-result fo-result--sub; tick Enable Calculation, Rounding 0.

( {Income:1} / 12 * {DTI:8} / 100 - {Debts:2} )

12. Principal & interest at that loan · Number · ID 12
Number Format Currency; Custom CSS Class (Appearance tab) fo-result fo-result--sub; tick Enable Calculation, Rounding 0.

if( {Rate:4} == 0 ):
( ( ( {Income:1} / 12 * {DTI:8} / 100 - {Debts:2} ) - {Down:3} * ( {Tax rate:6} / 1200 ) - {Insurance:7} / 12 ) / ( ( 1 / ( {Term:5} * 12 ) ) + ( {Tax rate:6} / 1200 ) ) ) * ( 1 / ( {Term:5} * 12 ) )
else:
( ( ( {Income:1} / 12 * {DTI:8} / 100 - {Debts:2} ) - {Down:3} * ( {Tax rate:6} / 1200 ) - {Insurance:7} / 12 ) / ( ( ( {Rate:4} / 1200 ) / ( 1 - ( 1 + ( {Rate:4} / 1200 ) ) ^ ( 0 - ( {Term:5} * 12 ) ) ) ) + ( {Tax rate:6} / 1200 ) ) ) * ( ( {Rate:4} / 1200 ) / ( 1 - ( 1 + ( {Rate:4} / 1200 ) ) ^ ( 0 - ( {Term:5} * 12 ) ) ) )
endif;

13. Email me these results · Section · ID 90
Description “One email with the numbers above, plus a link that brings them back.”; Custom CSS Class (Appearance tab) fo-email-results__head.

14. Your email · Email · ID 91
Description “Sent once, to this address only. No list, no follow-up.”; Custom CSS Class (Appearance tab) fo-email-results.

3. Email the results

This form submits once, to email the visitor their numbers. Three settings make it work, and the imported form already has them:

1. Notification (Form Settings → Notifications): “Results to the visitor”, sent to the Email field, with the inputs and results as merge tags such as {Home price:1} and a link back to the page.
2. Confirmation (Form Settings → Confirmations): type Redirect, to the page the form is on, with a query string that carries every input (fo1={Home price:1}&fo2=…). Point it at your own page.
3. Prepopulation: each input has “Allow field to be populated dynamically” on, with the parameter name fo plus its ID, so the redirect fills the form back in and the results reappear.

4. Put it on a page and make it look like this

Add the form to any page with the Gravity Forms block, or the shortcode [gravityform id="X" title="false" ajax="false"]. The form inherits your theme’s styles; the classes you set in step 2 are hooks for the look you see on this site:

• fo-result on a calculation field makes it the big teal result panel.
• fo-result fo-result--sub makes the smaller secondary figures.
• fo-segmented on a radio field turns it into a segmented switch.
• Two fields on one row is the editor’s own column layout: drag a field beside another and the row splits in half. No CSS class is needed, and the old gf_left_half Ready Classes are deprecated.

The bundle includes the two stylesheets that implement those classes, with notes on matching your brand colors. Without them the form still works; it just looks like your theme’s default Gravity Forms styling.

How the math works is explained under “How it’s calculated” on the live Mortgage affordability calculator.