Mortgage Overpayment or Savings Calculator

Compare mortgage overpayments with keeping accessible savings, including tax, charges and your cash reserve.

Your numbers stay in this browser tab. Nothing you enter is saved or submitted.

Your numbers

Illustrative figures to start. Change them to explore your decision.

Mortgage balance (£)

Mortgage interest rate (%)

Remaining term (months)20 years = 240 months

Monthly overpayment (£)

Lump-sum overpayment (£)

Gross savings AER (%)

Cash reserve, savings tax and lender terms

Cash currently available (£)

Emergency cash to retain (£)

Tax rate on savings interest (%)Use 0 for tax-free interest; account limits are not checked.

Unused annual savings allowance (£)Amount available to these savings after other interest. Use 0 if already used.

Upfront early repayment charge (£)

Current monthly payment (£)0 calculates the standard repayment. Keep an existing payment to model its actual path.

Your perspective

Debt freedom, with cash in view

Normal monthly payment£1,265.30Calculated standard: £1,265.30

Mortgage term saved62 months178 payments with overpayments

Mortgage interest saved£32,940.32£32,940.32 after the entered charge

Break-even gross savings AER5.16%Within the model’s 0–100% search range

Same cash budget. Same end date.

Overpay, then save freed payments £99,576.56

Normal payments, save spare cash £90,476.81

At month 240, overpaying then saving leaves £9,099.75 more cash. Both mortgages are cleared. That difference is conditional on constant rates, the entered tax allowance and saving all freed payments. Your £10,000.00 emergency reserve is kept out of both options.

Calculation breakdown
Normal mortgage interest	£103,671.63
Overpayment mortgage interest	£70,731.31
Savings-option gross interest	£35,994.98
Savings-option tax	£3,518.54
Savings-option net interest	£32,476.44
Upfront charge	£0.00

Monthly mortgage path

Monthly balances and overpayment interest
Month	Normal balance	Overpay balance	Overpay interest
1	£199,484.70	£189,247.20	£712.50
2	£198,967.47	£188,491.58	£709.68
3	£198,448.30	£187,733.12	£706.84
4	£197,927.18	£186,971.82	£704.00
5	£197,404.11	£186,207.66	£701.14
6	£196,879.08	£185,440.64	£698.28
7	£196,352.08	£184,670.74	£695.40
8	£195,823.10	£183,897.96	£692.52
9	£195,292.14	£183,122.28	£689.62
10	£194,759.19	£182,343.69	£686.71
11	£194,224.24	£181,562.18	£683.79
12	£193,687.28	£180,777.74	£680.86
13	£193,148.31	£179,990.36	£677.92
14	£192,607.32	£179,200.02	£674.96
15	£192,064.30	£178,406.72	£672.00
16	£191,519.24	£177,610.45	£669.03
17	£190,972.14	£176,811.19	£666.04
18	£190,422.99	£176,008.93	£663.04
19	£189,871.78	£175,203.66	£660.03
20	£189,318.50	£174,395.37	£657.01
21	£188,763.14	£173,584.05	£653.98
22	£188,205.70	£172,769.69	£650.94
23	£187,646.17	£171,952.28	£647.89
24	£187,084.54	£171,131.80	£644.82
25	£186,520.81	£170,308.24	£641.74
26	£185,954.96	£169,481.60	£638.66
27	£185,386.99	£168,651.86	£635.56
28	£184,816.89	£167,819.00	£632.44
29	£184,244.65	£166,983.02	£629.32
30	£183,670.27	£166,143.91	£626.19
31	£183,093.73	£165,301.65	£623.04
32	£182,515.03	£164,456.23	£619.88
33	£181,934.16	£163,607.64	£616.71
34	£181,351.11	£162,755.87	£613.53
35	£180,765.88	£161,900.90	£610.33
36	£180,178.45	£161,042.73	£607.13
37	£179,588.82	£160,181.34	£603.91
38	£178,996.98	£159,316.72	£600.68
39	£178,402.92	£158,448.86	£597.44
40	£177,806.63	£157,577.74	£594.18
41	£177,208.10	£156,703.36	£590.92
42	£176,607.33	£155,825.70	£587.64
43	£176,004.31	£154,944.75	£584.35
44	£175,399.03	£154,060.49	£581.04
45	£174,791.48	£153,172.92	£577.73
46	£174,181.65	£152,282.02	£574.40
47	£173,569.53	£151,387.78	£571.06
48	£172,955.12	£150,490.18	£567.70
49	£172,338.40	£149,589.22	£564.34
50	£171,719.37	£148,684.88	£560.96
51	£171,098.02	£147,777.15	£557.57
52	£170,474.34	£146,866.01	£554.16
53	£169,848.32	£145,951.46	£550.75
54	£169,219.95	£145,033.48	£547.32
55	£168,589.22	£144,112.06	£543.88
56	£167,956.13	£143,187.18	£540.42
57	£167,320.67	£142,258.83	£536.95
58	£166,682.82	£141,327.00	£533.47
59	£166,042.58	£140,391.68	£529.98
60	£165,399.94	£139,452.85	£526.47
61	£164,754.89	£138,510.50	£522.95
62	£164,107.42	£137,564.61	£519.41
63	£163,457.52	£136,615.18	£515.87
64	£162,805.19	£135,662.19	£512.31
65	£162,150.41	£134,705.62	£508.73
66	£161,493.17	£133,745.47	£505.15
67	£160,833.47	£132,781.72	£501.55
68	£160,171.30	£131,814.35	£497.93
69	£159,506.64	£130,843.35	£494.30
70	£158,839.49	£129,868.71	£490.66
71	£158,169.84	£128,890.42	£487.01
72	£157,497.68	£127,908.46	£483.34
73	£156,823.00	£126,922.82	£479.66
74	£156,145.79	£125,933.48	£475.96
75	£155,466.04	£124,940.43	£472.25
76	£154,783.74	£123,943.66	£468.53
77	£154,098.88	£122,943.15	£464.79
78	£153,411.45	£121,938.89	£461.04
79	£152,721.44	£120,930.86	£457.27
80	£152,028.85	£119,919.05	£453.49
81	£151,333.66	£118,903.45	£449.70
82	£150,635.86	£117,884.04	£445.89
83	£149,935.44	£116,860.81	£442.07
84	£149,232.40	£115,833.74	£438.23
85	£148,526.72	£114,802.82	£434.38
86	£147,818.40	£113,768.03	£430.51
87	£147,107.42	£112,729.36	£426.63
88	£146,393.77	£111,686.80	£422.74
89	£145,677.45	£110,640.33	£418.83
90	£144,958.44	£109,589.93	£414.90
91	£144,236.73	£108,535.59	£410.96
92	£143,512.32	£107,477.30	£407.01
93	£142,785.19	£106,415.04	£403.04
94	£142,055.33	£105,348.80	£399.06
95	£141,322.74	£104,278.56	£395.06
96	£140,587.40	£103,204.30	£391.04
97	£139,849.30	£102,126.02	£387.02
98	£139,108.43	£101,043.69	£382.97
99	£138,364.79	£99,957.30	£378.91
100	£137,618.36	£98,866.84	£374.84
101	£136,869.13	£97,772.29	£370.75
102	£136,117.09	£96,673.64	£366.65
103	£135,362.23	£95,570.87	£362.53
104	£134,604.54	£94,463.96	£358.39
105	£133,844.01	£93,352.90	£354.24
106	£133,080.63	£92,237.67	£350.07
107	£132,314.38	£91,118.26	£345.89
108	£131,545.26	£89,994.65	£341.69
109	£130,773.25	£88,866.83	£337.48
110	£129,998.35	£87,734.78	£333.25
111	£129,220.54	£86,598.49	£329.01
112	£128,439.82	£85,457.93	£324.74
113	£127,656.17	£84,313.10	£320.47
114	£126,869.58	£83,163.97	£316.17
115	£126,080.04	£82,010.53	£311.86
116	£125,287.54	£80,852.77	£307.54
117	£124,492.07	£79,690.67	£303.20
118	£123,693.62	£78,524.21	£298.84
119	£122,892.17	£77,353.38	£294.47
120	£122,087.72	£76,178.16	£290.08
121	£121,280.25	£74,998.53	£285.67
122	£120,469.75	£73,814.47	£281.24
123	£119,656.21	£72,625.97	£276.80
124	£118,839.62	£71,433.02	£272.35
125	£118,019.97	£70,235.59	£267.87
126	£117,197.24	£69,033.67	£263.38
127	£116,371.43	£67,827.25	£258.88
128	£115,542.52	£66,616.30	£254.35
129	£114,710.50	£65,400.81	£249.81
130	£113,875.36	£64,180.76	£245.25
131	£113,037.09	£62,956.14	£240.68
132	£112,195.68	£61,726.93	£236.09
133	£111,351.11	£60,493.11	£231.48
134	£110,503.38	£59,254.66	£226.85
135	£109,652.47	£58,011.56	£222.20
136	£108,798.37	£56,763.80	£217.54
137	£107,941.06	£55,511.36	£212.86
138	£107,080.54	£54,254.23	£208.17
139	£106,216.79	£52,992.38	£203.45
140	£105,349.80	£51,725.80	£198.72
141	£104,479.56	£50,454.47	£193.97
142	£103,606.06	£49,178.37	£189.20
143	£102,729.28	£47,897.49	£184.42
144	£101,849.21	£46,611.81	£179.62
145	£100,965.84	£45,321.30	£174.79
146	£100,079.16	£44,025.95	£169.95
147	£99,189.16	£42,725.75	£165.10
148	£98,295.82	£41,420.67	£160.22
149	£97,399.13	£40,110.70	£155.33
150	£96,499.08	£38,795.82	£150.42
151	£95,595.65	£37,476.00	£145.48
152	£94,688.83	£36,151.24	£140.54
153	£93,778.61	£34,821.51	£135.57
154	£92,864.98	£33,486.79	£130.58
155	£91,947.92	£32,147.07	£125.58
156	£91,027.42	£30,802.32	£120.55
157	£90,103.47	£29,452.53	£115.51
158	£89,176.06	£28,097.68	£110.45
159	£88,245.17	£26,737.75	£105.37
160	£87,310.79	£25,372.72	£100.27
161	£86,372.91	£24,002.57	£95.15
162	£85,431.51	£22,627.28	£90.01
163	£84,486.58	£21,246.83	£84.85
164	£83,538.10	£19,861.21	£79.68
165	£82,586.07	£18,470.39	£74.48
166	£81,630.47	£17,074.35	£69.26
167	£80,671.28	£15,673.08	£64.03
168	£79,708.50	£14,266.55	£58.77
169	£78,742.11	£12,854.75	£53.50
170	£77,772.09	£11,437.66	£48.21
171	£76,798.44	£10,015.25	£42.89
172	£75,821.13	£8,587.51	£37.56
173	£74,840.16	£7,154.41	£32.20
174	£73,855.51	£5,715.94	£26.83
175	£72,867.17	£4,272.07	£21.43
176	£71,875.12	£2,822.79	£16.02
177	£70,879.35	£1,368.08	£10.59
178	£69,879.85	£0.00	£5.13
179	£68,876.60	£0.00	£0.00
180	£67,869.59	£0.00	£0.00
181	£66,858.80	£0.00	£0.00
182	£65,844.22	£0.00	£0.00
183	£64,825.84	£0.00	£0.00
184	£63,803.64	£0.00	£0.00
185	£62,777.60	£0.00	£0.00
186	£61,747.72	£0.00	£0.00
187	£60,713.97	£0.00	£0.00
188	£59,676.35	£0.00	£0.00
189	£58,634.84	£0.00	£0.00
190	£57,589.42	£0.00	£0.00
191	£56,540.08	£0.00	£0.00
192	£55,486.81	£0.00	£0.00
193	£54,429.59	£0.00	£0.00
194	£53,368.40	£0.00	£0.00
195	£52,303.23	£0.00	£0.00
196	£51,234.07	£0.00	£0.00
197	£50,160.90	£0.00	£0.00
198	£49,083.70	£0.00	£0.00
199	£48,002.46	£0.00	£0.00
200	£46,917.17	£0.00	£0.00
201	£45,827.81	£0.00	£0.00
202	£44,734.36	£0.00	£0.00
203	£43,636.81	£0.00	£0.00
204	£42,535.15	£0.00	£0.00
205	£41,429.36	£0.00	£0.00
206	£40,319.42	£0.00	£0.00
207	£39,205.32	£0.00	£0.00
208	£38,087.04	£0.00	£0.00
209	£36,964.57	£0.00	£0.00
210	£35,837.89	£0.00	£0.00
211	£34,706.98	£0.00	£0.00
212	£33,571.83	£0.00	£0.00
213	£32,432.42	£0.00	£0.00
214	£31,288.74	£0.00	£0.00
215	£30,140.77	£0.00	£0.00
216	£28,988.50	£0.00	£0.00
217	£27,831.91	£0.00	£0.00
218	£26,670.98	£0.00	£0.00
219	£25,505.70	£0.00	£0.00
220	£24,336.05	£0.00	£0.00
221	£23,162.01	£0.00	£0.00
222	£21,983.57	£0.00	£0.00
223	£20,800.71	£0.00	£0.00
224	£19,613.41	£0.00	£0.00
225	£18,421.66	£0.00	£0.00
226	£17,225.44	£0.00	£0.00
227	£16,024.74	£0.00	£0.00
228	£14,819.53	£0.00	£0.00
229	£13,609.80	£0.00	£0.00
230	£12,395.54	£0.00	£0.00
231	£11,176.72	£0.00	£0.00
232	£9,953.33	£0.00	£0.00
233	£8,725.35	£0.00	£0.00
234	£7,492.77	£0.00	£0.00
235	£6,255.57	£0.00	£0.00
236	£5,013.73	£0.00	£0.00
237	£3,767.23	£0.00	£0.00
238	£2,516.06	£0.00	£0.00
239	£1,260.20	£0.00	£0.00
240	£0.00	£0.00	£0.00

A worked example

With £1,200 remaining, zero interest and 12 months to run, the normal payment is £100. Adding £100 a month clears the balance in six months. No interest is saved at 0%: the benefit is earlier repayment, not a financial return.

What this calculation assumes

Repayment mortgage; fixed rate throughout, monthly interest at annual rate ÷ 12, payments at month-end, rounded to pennies. Real lenders may use daily interest and different recalculation rules. Interest-only mortgages are not supported.
Both options use the same monthly budget until the normal mortgage clears. The savings option retains the proposed lump sum and the charge avoided. The overpayment option saves its freed monthly payments after clearing the mortgage. Unused cash and your emergency reserve are common to both and excluded from the comparison.
Savings use a constant gross AER, monthly compounding and deposits at month-end. Tax is deducted after each 12-month modelling period and at the end, using your stated unused annual allowance. These periods are not calendar tax years. Enter zero tax for an eligible tax-free account; capacity and eligibility are not checked.
The charge is paid upfront from cash, once. Check your lender’s overpayment allowance and actual charges. No future rate changes, inflation, remortgage fees or pension alternatives are forecast. Break-even is the modelled gross savings AER, including the entered tax position and charge.

Sources and rules

Rules and guidance checked 5 October 2026. Rates entered in mortgage, debt and car comparisons are your assumptions, not live offers.

Put the numbers in perspective

Illustrative information, not personal financial, tax or debt advice. Check your circumstances and contractual terms before acting. Read our disclaimer.